A.1.2 Measuring equipment
A.1.2.1
Instruments and auxiliary devices for the external examination:
magnifying glasses with at least magnification ;
graduated scales or gauges for checking dimensions.
A.1.2.2
Instruments and auxiliary devices for determining the errors of indication.
A.1.2.2.1
Well-stirred water baths with interchangeable thermometer-holders. The thermometers under examination must be immersed in the bath to the lowest numbered line on the scale.
During measurement, the temperature of the water baths must be constant to within and uniform to within better than .
The use of baths with automatic temperature control is recommended.
There must be enough water to ensure that immersion of the thermometers in the bath will not cause a temperature drop greater than . Time can be saved when testing by preheating the thermometers in a special bath to a few tenths of a degree Celsius below the test temperature.
A.1.2.2.2
Standard thermometers, e.g., total immersion mercury-in-glass thermometers with scale intervals of or and an auxiliary scale for , or platinum resistance thermometers.
Preferably two standards thermometers are used to measure the temperature of the baths (A.3.1) and a third standard thermometer to check the first two.
The corrections for standard thermometers, including the correction at must be determined to within an uncertainty of measurement of preferably or a maximum .
A.1.2.2.3
Magnifying glasses with at least magnification for reading standard enclosedscale mercury-in-glass thermometers.
Monocular or binocular viewers with approximately magnification for reading standard solid-stem mercury-in-glass thermometers.
A.1.2.2.4
A centrifuge with a container for thermometers to drive down the mercury column in thermometers under test. The centrifuge must be capable of exerting an acceleration of on the mercury at the level of the base of the thermometer bulbs (see 5.4).
A.1.2.2.5
A zero point () ice bath for testing standard thermometers3). The device consists of a Dewar flask filled with finely crushed ice covered over with water. The water used to make the ice and the water in which the ice is submerged must be pure. Its electrical conductivity must not exceed at . The ice must be carefully tamped so that there are no air bubbles in the ice-water mixture. It must be compacted as much as possible both prior to measurement and periodically during measurement.
It is recommended that a water purifier, a refrigerator with ice trays, and an ice crusher be obtained for preparing the ice-water mixture.