The TBK-HP Test Block for HP Textile Durometers with Flat Base, 2 blocks in fitted case is for periodic verification for HP Textile Durometers with flat bases (models HP-5F and HP-10F). The test block kits gives the user the ability to develop the proper "feel", and, while they are not to be used for calibration purposes, they enable the user to perform a quick check for proper durometer operation. A large variation would indicate the need for recalibration of the durometer being utilized.