IMIN - Measurement instruments

This document applies to water meters used to meter the volume of cold potable water and hot water flowing through a fully charged, closed conduit. These water meters incorporate devices which indicate the integrated volume.
This document specifies criteria for the selection of single, combination and concentric water meters, associated fittings, installation, special requirements for meters, and the first operation of new or repaired meters to ensure accurate constant measurement and reliable reading of the meter.
In addition to meters based on mechanical principles, this document also applies to water meters based on electrical or electronic principles, and to water meters based on mechanical principles incorporating electronic devices, used to measure the volume of cold potable water and hot water. It also applies to electronic ancillary devices. Ancillary devices are optional. However, national or international regulations may make some ancillary devices mandatory in relation to the utilization of the water meter.
The recommendations of this document apply to water meters, irrespective of technology, defined as integrating measuring instruments determining the volume of water flowing through them.
NOTE            Any national regulations apply in the country of use.

This document specifies the metrological and technical requirements for water meters for cold potable water and hot water flowing through a fully charged, closed conduit. These water meters incorporate devices which indicate the accumulated volume.
In addition to water meters based on mechanical principles, this document applies to devices based on electrical or electronic principles, and mechanical principles incorporating electronic devices, used to measure the volume of cold potable water and hot water.
This document also applies to electronic ancillary devices. Ancillary devices are optional. However, it is possible for national or regional regulations to render some ancillary devices mandatory in relation to the utilization of water meters.
NOTE            Any national regulations apply in the country of use.

This document is applicable to the type evaluation and initial verification testing of water meters for cold potable water and hot water as defined in ISO 4064-1:2024|OIML R 49‑1:2024. OIML Certificates of conformity can be issued for water meters under the scope of the OIML Certificate System, provided that this document, ISO 4064-1:2024|OIML R 49‑1:2024 and ISO 4064-3:2024|OIML R 49‑3:2024 are used in accordance with the rules of the system.
This document sets out details of the test programme, principles, equipment and procedures to be used for the type evaluation, and initial verification of a meter type.
The provisions of this document also apply to ancillary devices, if required by national regulations.
The provisions include requirements for testing the complete water meter and for testing the measurement transducer (including the flow or volume sensor) and the calculator (including the indicating device) of a water meter as separate units.

This document applies to water meters used to meter the volume of cold potable water and hot water flowing through a fully charged, closed conduit. These water meters incorporate devices which indicate the integrated volume.
This document specifies technical characteristics and pressure loss requirements for meters for cold potable water and hot water. It applies to water meters which can withstand:
a)       a maximum admissible pressure (MAP) equal to at least 1 MPa1) [0,6 MPa for meters for use with pipe nominal diameters (DNs) ≥500 mm];
b)       a maximum admissible temperature (MAT) for cold potable water meters of 30 °C;
c)        a MAT for hot water meters of up to 180 °C, depending on class.
In addition to meters based on mechanical principles, this document also applies to water meters based on electrical or electronic principles, and to water meters based on mechanical principles incorporating electronic devices, used to meter the volume flow of hot water and cold potable water. It also applies to electronic ancillary devices. As a rule ancillary devices are optional. However, national or international regulations may make some ancillary devices mandatory in relation to the utilization of the water meter.
1) 1 MPa = 10 bar (1 bar = 0,1 MPa =105 Pa; 1 MPa = 1 N/mm2).

This document specifies a test report format to be used in conjunction with ISO 4064-1:2024|OIML R 49-1:2024 and ISO 4064-2:2024|OIML R 49-2:2024 for water meters for cold potable water and hot water.

This document provides guidance on the collation of the measurements required for the management of siltation at river structures. These include structures used by water supply utilities, other major water abstractors, HEP producers, and for flow measurement by environmental protection agencies.
The document is also intended for use when a redundant structure is being removed, or when modifications to a structure are being made to facilitate fish migration or for river restoration. This is to ensure that the impacts of these changes are adequately monitored and recorded.
The document covers the provision of routine measurements, and the checks and requirements that need to be made by the operator so that specific basic information is collated and made readily available. This information is used to inform decision-making by environment management agencies that authorise flushing, sediment clearance or sedimentation removal. This is to ensure minimal environmental impacts, and to compliance with existing environmental legislation.

Non-catching type gauges are the emerging class of in situ precipitation measurement instruments. For these instruments, rigorous testing and calibration are more challenging than for traditional gauges. Hydrometeors’ characteristics like particle size, shape, fall velocity and density need to be reproduced in a controlled environment to provide the reference precipitation, instead of the equivalent water flow used for catching-type gauges. They are generally calibrated by the manufacturers using internal procedures developed for the specific technology employed. No agreed methodology exists, and the adopted procedures are rarely traceable to internationally recognized standards. This document describes calibration and accuracy issues of non-catching instruments used for liquid/solid atmospheric precipitation measurement. An overview of the existing models of non-catching type instruments is included, together with an overview and a description of their working principles and the adopted calibration procedures. The literature and technical manuals disclosed by manufacturers are summarized and discussed, while current limitations and metrological requirements are identified.

This document specifies general requirements, minimum performance requirements and test procedures for open channel instrumentation used to determine either volumetric flow-rate and/or total volume passed of waters in artificial open channels. It covers the following technology categories:
- Level sensors with associated electronics designed to be used with a conventional gauging structure. (The requirements and test procedures for gauging structures, such as weirs and flumes, are excluded. The stage discharge characteristics for many of these structures are established and published in national and international standards).
- Water velocity sensors.
- Integrated velocity area instruments comprising level and velocity sensors that may be separate or combined in a single assembly.
- Velocity sensors that determine the mean water velocity through a channel.
It is recognized that for some OCIs, certain tests cannot be carried out.

This document specifies general requirements, minimum performance requirements and test procedures for instrumentation used to measure either volumetric flow-rate and/or total volume passed of water in closed conduits. It covers all closed conduit instrument (CCI) technologies intended to operate in closed pressurized pipes and partially filled pipes. Requirements are expressed in volumetric units which may be converted to mass using the density of the water.
It is recognized that for some CCIs certain tests cannot be carried out.
The data obtained from the testing of CCIs in accordance with the requirements of the Measuring Instruments Directive [1] or EN ISO 4064-1 [2] can be used to meet, in part, the requirements specified in this document. However, for the avoidance of doubt, compliance with the requirements of this document does not equate to compliance with the requirements of the Measuring Instruments Directive or EN ISO 4064-1.

This document specifies definitions, requirements and testing of additional functionalities for water meters, without metrological impact, in combination with Additional Functionality Devices (AFD) and in response to EU/EFTA Mandate M/441 EN. These AFDs are considered as “ancillary devices” as defined in EN ISO 4064-1:2017 and EN ISO 4064-4:2014.
This document does not cover the changing of metrological software within the meter or the upload/download of metrological software.
NOTE   A manufacturer can claim compliance only for additional functionalities described in this document. It is not mandatory that an AFD complies with all additional functionalities described herein.

This document defines the requirements for on-site measurements of snow depth and depth of snowfall. This document provides guidance on manual and automatic measuring techniques, and information about sources of errors and measurement uncertainty.

This document provides an understanding of the nature of measurement uncertainty and its significance in estimating the "quality" of a measurement or a determination in hydrometry.
This document is applicable to flow measurements in natural and man-made channels. Rainfall measurements are not covered.

This document specifies the geometry and method of use (installation and operating conditions) of cone meters when they are inserted in a conduit running full to determine the flow rate of the fluid flowing in the conduit.
As the uncertainty of an uncalibrated cone meter might be too high for a particular application, it might be deemed essential to calibrate the flow meter in accordance with Clause 7.
This document also provides background information for calculating the flow rate and is applicable in conjunction with the requirements given in ISO 5167‑1.
This document is applicable only to cone meters in which the flow remains subsonic throughout the measuring section and where the fluid can be considered as single-phase. Uncalibrated cone meters can only be used within specified limits of pipe size, roughness, β, and Reynolds number, Re. This document is not applicable to the measurement of pulsating flow. It does not cover the use of uncalibrated cone meters in pipes sized less than 50 mm or more than 500 mm, or where the pipe Reynolds numbers are below 8 × 104 or greater than 1,2 × 107.
A cone meter is a primary device which consists of a cone-shaped restriction held concentrically in the centre of the pipe with the nose of the cone upstream. The design of cone meter defined in this document has one or more upstream pressure tappings in the wall, and a downstream pressure tapping positioned in the back face of the cone with the connection to a differential pressure transmitter being a hole through the cone to the support bar, and then up through the support bar.
Alternative designs of cone meters are available; however, at the time of writing, there is insufficient data to fully characterize these devices, and therefore, these meters shall be calibrated in accordance with Clause 7.

This document specifies the geometry and method of use (installation and operating conditions) of nozzles and Venturi nozzles when they are inserted in a conduit running full to determine the flowrate of the fluid flowing in the conduit.
This document also provides background information for calculating the flowrate and is applicable in conjunction with the requirements given in ISO 5167‑1.
This document is applicable to nozzles and Venturi nozzles in which the flow remains subsonic throughout the measuring section and where the fluid can be considered as single-phase. In addition, each of the devices can only be used within specified limits of pipe size and Reynolds number. It is not applicable to the measurement of pulsating flow. It does not cover the use of nozzles and Venturi nozzles in pipe sizes less than 50 mm or more than 630 mm, or where the pipe Reynolds numbers are below 10 000.
This document deals with
a) three types of standard nozzles:
1)    ISA 1932[1] nozzle;
2)    the long radius nozzle[2];
3)    the throat-tapped nozzle
b) the Venturi nozzle.
The three types of standard nozzle are fundamentally different and are described separately in this document. The Venturi nozzle has the same upstream face as the ISA 1932 nozzle, but has a divergent section and, therefore, a different location for the downstream pressure tappings, and is described separately. This design has a lower pressure loss than a similar nozzle. For all of these nozzles and for the Venturi nozzle direct calibration experiments have been made, sufficient in number, spread and quality to enable coherent systems of application to be based on their results and coefficients to be given with certain predictable limits of uncertainty.
[1]   ISA is the abbreviation for the International Federation of the National Standardizing Associations, which was superseded by ISO in 1946.
[2] The long radius nozzle differs from the ISA 1932 nozzle in shape and in the position of the pressure tappings.

This document specifies the geometry and method of use (installation and operating conditions) of wedge meters when they are inserted in a conduit running full to determine the flow rate of the fluid flowing in the conduit.
NOTE 1    As the uncertainty of an uncalibrated wedge meter can be too large for a particular application, it could be deemed essential to calibrate the flow meter according to Clause 7.
This document gives requirements for calibration which, if applied, are for use over the calibrated Reynolds number range. Clause 7 could also be useful guidance for calibration of meters of similar design but which fall outside the scope of this document.
It also provides background information for calculating the flow rate and is applicable in conjunction with the requirements given in ISO 5167‑1.
This document is applicable only to wedge meters in which the flow remains subsonic throughout the measuring section and where the fluid can be considered as single-phase. Uncalibrated wedge meters can only be used within specified limits of pipe size, roughness, β (or wedge ratio) and Reynolds number. It is not applicable to the measurement of pulsating flow. It does not cover the use of uncalibrated wedge meters in pipes whose internal diameter is less than 50 mm or more than 600 mm, or where the pipe Reynolds numbers are below 1 × 104.
NOTE 2    A wedge meter has a primary element which consists of a wedge-shaped restriction of a specific geometry. Alternative designs of wedge meters are available; however, at the time of writing there is insufficient data to fully characterize these devices, and therefore these meters are calibrated in accordance with Clause 7.

This document defines terms and symbols and establishes the general principles for methods of measurement and computation of the flow rate of fluid flowing in a conduit by means of pressure differential devices (orifice plates, nozzles, Venturi tubes, cone meters, and wedge meters) when they are inserted into a circular cross-section conduit running full. This document also specifies the general requirements for methods of measurement, installation and determination of the uncertainty of the measurement of flow rate.
ISO 5167 (all parts) is applicable only to flow that remains subsonic throughout the measuring section and where the fluid can be considered as single-phase. It is not applicable to the measurement of pulsating flow.

This document specifies the geometry and method of use (installation in a system and operating conditions) of critical flow nozzles (CFNs) used to determine the mass flow rate of a gas flowing through a system basically without the need to calibrate the CFN. It also gives the information necessary for calculating the flow rate and its associated uncertainty.
This document is applicable to nozzles in which the gas flow accelerates to the critical velocity at the minimum flowing section, and only where there is steady flow of single-phase gas. When the critical velocity is attained in the nozzle, the mass flow rate of the gas flowing through the nozzle is the maximum possible for the existing inlet condition, while the CFN can only be used within specified limits, e.g. the CFN throat to inlet diameter ratio and Reynolds number. This document deals with the toroidal- and cylindrical-throat CFNs for which direct calibration experiments have been made in sufficient number to enable the resulting coefficients to be used with certain predictable limits of uncertainty.

This document specifies the geometry and method of use (installation and operating conditions) of orifice plates when they are inserted in a conduit running full to determine the flow rate of the fluid flowing in the conduit.
This document also provides background information for calculating the flow rate and is applicable in conjunction with the requirements given in ISO 5167‑1.
This document is applicable to primary devices having an orifice plate used with flange pressure tappings, or with corner pressure tappings, or with D and D/2 pressure tappings. Other pressure tappings such as “vena contracta” and pipe tappings are not covered by this document. This document is applicable only to a flow which remains subsonic throughout the measuring section and where the fluid can be considered as single phase. It is not applicable to the measurement of pulsating flow[1]. It does not cover the use of orifice plates in pipe sizes less than 50 mm or more than 1 000 mm, or where the pipe Reynolds numbers are below 5 000.

This document specifies the geometry and method of use (installation and operating conditions) of Venturi tubes[1] when they are inserted in a conduit running full to determine the flow rate of the fluid flowing in the conduit.
This document also provides background information for calculating the flow rate and is applicable in conjunction with the requirements given in ISO 5167-1.
This document is applicable only to Venturi tubes in which the flow remains subsonic throughout the measuring section and where the fluid can be considered as single-phase. In addition, Venturi tubes can only be used uncalibrated in accordance with this standard within specified limits of pipe size, roughness, diameter ratio and Reynolds number, or alternatively they can be used across their calibrated range. This document is not applicable to the measurement of pulsating flow. It does not cover the use of uncalibrated Venturi tubes in pipes sized less than 50 mm or more than 1 200 mm, or where the pipe Reynolds numbers are below 2 × 105.
This document deals with the three types of classical Venturi tubes:
a) “as cast”;
b) machined;
c) fabricated (also known as “rough-welded sheet-iron”).
A Venturi tube consists of a convergent inlet connected to a cylindrical throat which is in turn connected to a conical expanding section called the divergent section (or alternatively the diffuser). Venturi nozzles (and other nozzles) are dealt with in ISO 5167-3.
NOTE       In the USA the classical Venturi tube is sometimes called the Herschel Venturi tube.
[1]   In the USA the classical Venturi tube is sometimes called the Herschel Venturi tube.

This document specifies the functional requirements of instrumentation for measuring the level of water surface (stage), primarily for the purpose of determining flow rates.
This document is supplemented by Annex A, which provides guidance on the types of automatic water level measurement devices currently available and the measurement uncertainty associated with them. The manually operated measuring devices are described in Annex B.
This document is applicable to both contact and non-contact methods of measurement. The non-contact methods are not in direct material contact with the water surface but measure the height of the water level with ultrasonic or electromagnetic waves.

This Technical Report (TR) provides guidance to assist with the planning and design of Hydrometric networks, to ensure a better understanding of the water cycle, and that any data are observed and collated in an effective and appropriate manner. The TR is intended for use when:-
• a new network is being planned and designed;
• the nature, value and extent of an existing network is being reviewed;
• a redundant network is being decommissioned or modified.
This is to ensure that the impacts of these changes are considered objectively, and all changes are adequately monitored and recorded.
This TR covers all aspects that are considered pertinent to the evaluation. The information will be used to inform the decision-making process employed by the network’s owners and operators. The objective nature of the review will ensure that all influential factors, both beneficial and otherwise, are considered. This will ensure that primary and potential alternative uses of the network are considered. It will also ensure compliance with any extant environmental legislation.

This document defines terms and symbols used in standards in the field of hydrometry.

This document specifies methods for determining the velocity and cross-sectional area of water flowing in open channels and for calculating the discharge employing point velocity measurement devices.
It is applicable to methods using rotating-element current meters, acoustic doppler velocimeters (ADVs), acoustic doppler current profiler (ADCP) stationary method, surface velocity measurement including floats and other surface velocity systems.
Although some general procedures are discussed, this document does not describe in detail how to use or deploy these systems.
NOTE         For detailed procedures, refer to guidelines from instrument manufacturers and the appropriate public agencies.

This document specifies a calibration method for mechanical type, electromagnetic type and acoustic type hydrometric current-meters used for point velocity measurement of flowing water. The method requires towing the instrument through still water in a straight open tank. It includes measuring apparatus, the calibration procedure, the method of presenting the results and the uncertainties associated with the method.

This document considers liquid atmospheric precipitation and defines the procedures and equipment to perform laboratory and field tests, in steady-state conditions, for the calibration, check and metrological confirmation of liquid precipitation measurement instruments. It provides a classification of catching-type measurement instruments based on their laboratory performance. The classification does not relate to the physical principle used for the measurement, nor does it refer to the technical characteristics of the instrument assembly, but is solely based on the instrument calibration. Attribution of a given class to an instrument is not intended as a high/low ranking of its quality but rather as a quantitative standardized method to declare the achievable measurement accuracy in order to provide guidance on the suitability for a particular purpose, while meeting the user’s requirements.

ISO 20456:2017 applies to industrial electromagnetic flowmeters used for the measurement of flowrate of a conductive liquid in a closed conduit running full. It covers flowmeter types utilizing both alternating current (AC) and pulsed direct current (DC) circuits to drive the field coils and meters running from a mains power supply and those operating from batteries or other sources of power.
ISO 20456:2017 is not applicable to insertion-type flowmeters or electromagnetic flowmeters designed to work in open channels or pipes running partially full, nor does it apply to the measurement of magnetically permeable slurries or liquid metal applications.
ISO 20456:2017 does not specify safety requirements in relation to hazardous environmental usage of the flowmeter.

ISO 20456:2017 applies to industrial electromagnetic flowmeters used for the measurement of flowrate of a conductive liquid in a closed conduit running full. It covers flowmeter types utilizing both alternating current (AC) and pulsed direct current (DC) circuits to drive the field coils and meters running from a mains power supply and those operating from batteries or other sources of power.
ISO 20456:2017 is not applicable to insertion-type flowmeters or electromagnetic flowmeters designed to work in open channels or pipes running partially full, nor does it apply to the measurement of magnetically permeable slurries or liquid metal applications.
ISO 20456:2017 does not specify safety requirements in relation to hazardous environmental usage of the flowmeter.

This document gives recommendations for the management of observed hydrometric data, including raw data and other data as well as statistics derived from these observations. Although the principles of data management can be applied to all hydrometric observations, particular focus is placed on measurements of precipitation, water level (including stage), volume and discharge in open channels.
NOTE   The range of sites where water levels, and sometimes flow, are measured includes lakes, reservoirs, rivers, canals, tidal waters, sewers, wells, and boreholes.
The document covers metadata associated with hydrometric data, including recommendations for the production and management of descriptive, analytical and statistical material relating to sites where and measuring techniques, by which hydrometric data are collected. The recommendations of this document can be applied to some forms of data directly derived from observational records (for example, summary time series of monthly mean river flows). While not primarily designed for the management of data resulting from more complex numerical models or spatially aggregated data sets (for example, remotely-sensed data), many of the recommendations are applicable for such types of data.
This document does not cover the field collection of data or its transmission, but focuses on the management of data once they have been received in a hydrometric information management system.

ISO 1438:2017 defines the requirements for the use of rectangular and triangular (V-notch) thin-plate weirs for the measurement of flow of clear water in open channels under free flow conditions. It includes the requirements for the use of full-width rectangular thin-plate weirs in submerged (drowned) flow conditions.

ISO 6416 describes the establishment and operation of an ultrasonic (transit-time) gauging station for the continuous measurement of discharge in a river, an open channel or a closed conduit. It also describes the basic principles on which the method is based, the operation and performance of associated instrumentation and procedures for commissioning.
It is limited to the "transit time of ultrasonic pulses" technique, and is not applicable to systems that make use of the "Doppler shift" or "correlation" or "level-to-flow" techniques.
ISO 6416 is not applicable to measurement in rivers with ice.
NOTE       ISO 6416 focuses on open channel flow measurement. IEC 60041 covers the use of the technique for full pipe flow measurement.

This European Standard has been adapted from the OIML Recommendation R 76-1, Edition 2006, Non-automatic weighing instruments Part 1 - Metrological and technical requirements – Tests by a Joint Working Group from CEN and CENELEC. It was elaborated following a standardization request from the Commission of the European Communities to CEN and CENELEC to establish a European Standards related to Council Directive 2009/23/EC on Non-automatic weighing instruments.

ISO 15769:2010 provides guidelines on the principles of operation and the selection and use of Doppler-based and echo correlation velocity meters for continuous-flow gauging.
ISO 15769:2010 is applicable to channel flow determination in open channels and partially filled pipes using one or more meters located at fixed points in the cross-section.

ISO 4375:2014 defines the requirements for equipment, anchorage, supports and accessories for cableway systems for use in stream gauging. Systems which are operated either entirely from the river bank or from a suspended personnel carriage (also called a "cable car") are discussed. Should the cableway installation be required to be certified as lifting equipment, other standards or regulations may apply. ISO 4375:2014 is only applicable to the cableway systems to be used for hydrometric measurements.

This Technical Report defines the requirements for manual measurements of SWE over land, see ice and glaciers, under natural environmental conditions, and shows methods for calculating the spatial distribution of the data. It includes measurements with snow tubes, core drills and density cutters.

ISO 18365:2013 gives requirements for the establishment and operation of a gauging station for the measurement of stage, or stage and discharge, of a lake, reservoir, river or canal or other artificial open channel. It also describes how a gauging station utilising one of the measurement methods listed should be operated and maintained.
Requirements are provided for stage only measurement stations, stage-discharge stations and direct-discharge measurement stations in natural channels, as well as for stage-discharge stations with artificial structures. Additionally, some requirements are given for measurements under difficult conditions, such as under ice conditions.

This Technical Report describes a method for calibrating rainfall intensity (RI) gauges and the measurement requirements to obtain accurate and compatible data sets from hydro-meteorological networks, as a forerunner to the development of full hydro-meteorological data collection standards.
This Technical Report deals exclusively with catching-type RI gauges (see Clause 3). It concentrates on the generic calibration, performance checking and estimation of uncertainties for RI gauges. It does not cover specific gauge measurement principles, technical characteristics and technology adopted in the design of RI gauges.

Describes the tracers used (fluorescein, rhodamine B, acid yellow 7, sulfo rhodamine B, pyranine, and rhodamine WT), the tracer measurement (principle, field measurement and laboratory measurements), environmental factors affecting tracers, techniques for tracer injection, sampling techniques, analysis and computation.

Describes the tracers used (iodide, lithium, chloride, chromium), the tracer measurement (principle, field measurement and laboratory measurements), environmental factors affecting tracers, techniques for tracer injection, sampling techniques, analysis and sources of error.

ISO 1088:2007 provides a standard basis for the collection and processing of data for the determination of the uncertainties in measurements of discharge in open channels by velocity-area methods using current meters. To determine the discharge in open channels by the velocity-area method, components of the flow (velocity, depth and breadth) need to be measured. The component measurements are combined to compute the total discharge. The total uncertainty in the computed discharge is a combination of the uncertainties in the measured components.
ISO 1088:2007 is intended to be applied to velocity-area methods that involve measurement of point velocities at a relatively small number of discrete depths and transverse positions in the flow cross-section, as described in ISO 748. It is not intended to be applied to measurements made by Acoustic Doppler Velocity Profilers (ADVP) or other instruments that produce essentially continuous velocity profiles of the flow field.

Concerns principles of the constant rate injection method and the sudden injection method (integration method), and the principles of injection, sampling and analysis which apply for all types of tracer. The tracers used and their concentrations should be compatible with the legislation of each country regarding the occasional and short-durations discharges of foreign substances into natural waters.

This European Standard applies to breath alcohol test devices which measure the concentration of alcohol contained in an exhaled breath sample intended to be used for screening or preliminary testing. This standard specifies requirements for basic safety and performance, test methods and requirements for marking, labelling and operating instructions.
This standard gives guidelines for type approval procedure consisting of a number of technical performance tests, but excluding in vivo tests, that are carried out on devices supplied by the manufacturers.
In vivo tests, which are designed to test the ability of the device to work with real subjects, may be arranged in compliance with national requirements.
This standard is not applicable to devices covered by OIML R 126:1998 (Evidential breath analyzers) or single use testers.
Devices are designed for law enforcement.

This European Standard specifies the design of a reference raingauge pit. The reference raingauge pit is designed for the liquid precipitation only. The specified details of the pit and the grating, are purposely kept to a minimum in order to allow each raingauge operator latitude in their construction and to suit local conditions.

This Technical Report defines the requirements for the use of snow mass registration devices for measurement of SWE under natural environmental conditions. It includes weighing and pressure measuring methods.