5.2. Test element
5.2.1. Meters must be designed in such a way that checking can be done with sufficient accuracy. For this purpose they must incorporate in their design an integral test unit or arrangements permitting the connection of a portable test unit.
5.2.2. The integral test element may be the last element of the counter in one of the two following forms:
(a) a continuously revolving drum carrying a graduated scale;
(b) a pointer passing over a fixed dial having a graduated scale or a disc carrying a graduated scale moving past a fixed reference mark.
5.2.3. On the graduated scales of these test elements the unit of the graduations must be indicated clearly and unambiguously in m3 or decimal submultiples of the m3 ; the beginning of the scale must be indicated by the figure zero.
In both cases (dial and digital indicators):
- the unit symbol m3 must be shown either on the dial or in the immediate vicinity of the digital indication,
- the fastest-moving and visually readable graduated element - "the control element" - must move continuously ; its scale interval is known as the verification scale interval. This control element may be permanent or may be fitted temporarily by adding detachable parts. These parts must not have any significant influence on the metrological properties of the meter.
