While these test blocks are a convenient form of comparative verification, they are not intended to be used for the purpose of durometer calibration. Rather, they are a form of “quick reference” to the operational status of the durometer being used. A large variation would indicate the need for recalibration of the durometer being utilized. This should be done in accordance with the methods indicated in ASTM D 2240.
The material (rubber) from which the test blocks are made is fairly stable, however, it is strongly recommended that calibration of these test blocks be verified annually.