The Series 3 Tacho Belt is a green rubber band required for the operation of the S3 monitor.
$7.50
AboutWRP-C290 - SIII (S3) Tacho Belt
SIII Tacho Belt Used For; Connects the Tacho Clutch Pulley to the Tacho Pulley on the SIII Monitor Used On; All S III Models Includes; SIII Tacho Belt Only