What about so called "adjustable gauges". How do they work?

A few manufacturers produce so called "adjustable" gauges. These gauges permit the indicator needle to be re-set to the zero point using a conventional jeweler's screwdriver inserted into the air inlet at the base of the gauge. ANSI/AAMI/ISO 81060 prohibits the manufacture of any instrument with an adjustable dial, except by use of a specialized tool. We hardly think a jeweler's screwdriver available from virtually any hardware store qualifies as a "specialized" tool.

Whether or not they are legal, we feel adjustable gauges can be dangerous! Although re-setting of the indicator needle to zero will occasionally re-calibrate a gauge, it often will not. The only way to ensure proper calibration, once adjusted, is to bench test the instrument at a variety of points on the dial against a unit of known accuracy. There is a strong tendency to skip this CRITICAL step when gauges are adjusted in the field since it is time consuming and inconvenient (not to mention tough to find a unit of known accuracy in the field). Since ADC provides free recalibration for a minimum of 5 years to as long as a lifetime, (depending on model) we suggest you let us perform this complimentary service.