These instruments count the number of revolutions of a mechanical part (e.g., machine shaft). They consist mainly of a driving spindle geared to pointer or drum indicators. They usually have a device for re-setting the counter to zero. The counters may be coupled to the revolving part either directly (in some cases the part drives the gearing itself) or by remote control. The driving spindle may be operated by a rotary, alternating or pulsating movement of the turning part (e.g., encoders).
yarn grading winding reels, torsiometers and similar testing or checking apparatus incorporating revolution counters (heading 90.31)