Highest degree of accuracy when used at a temperature of 68º F (20º C).  Each block serialized regardless of the grade for identification when block is re-calibrated and certified at a later date.  Alloy steel with Rockwell hardness of 65.  Sets are calibrated to meet or exceed federal specifications GGG-G-15C.  Grade "B" supplies with a certificate of accuracy only.  "Grade A+" is supplied with a certificate of calibration traceable to NBS.  Set is supplied in fitted case.