On Page 326, Section 20.2.3 Stressing, of the Post-Tensioning Institute's Post-Tensioning Manual, 6th edition, it says: Stressing equipment should be accompanied by calibration records that are no more than six months old and should indicate the proper hydraulic gauge pressure to which the tendons are to be stressed to achieve the required final effective force.
Page 89, Section 4.4.7.2.1 Stressing Equipment says: For each ram and gauge unit used on the job site, the post-tensioning supplier must furnish certified calibration charts to the Design Engineer prior to stressing. The post-tensioning supplier must further verify that ram and gauge serial numbers match those listed on the calibration sheets.