Just one reference that I could dig up quickly is from the AISC ref - AISCQC001 AISC 201-06 AISC Certification Program for Structural Steel Fabricators
14. Calibration of Inspection, Measuring, and Test Equipment
The Fabricator shall develop a Documented Procedure to control, calibrate, and maintain inspection, measuring, and test equipment used to demonstrate the compliance of products and processes to the specified requirements. Tools with devices for measuring properties of fabricated pieces or process variables are included in this requirement when they are used to demonstrate the compliance of products and processes to the specified requirements. The Procedure shall define equipment calibration frequency. However, the volt/amp meters used to verify compliance with WPS parameters (may be welding machine volt and amp meters or auxiliary volt/amp meters) shall be calibrated whenever the accuracy of the meter is in question and at a minimum every twelve months. Inspection, measuring and test equipment shall be used in a manner consistent with the required measurement. The precision capability of the equipment used shall support reliable determination of compliance with acceptance criteria. When specifically required, technical data pertaining to the measurement equipment shall be made available for verification that the measuring equipment is performing properly.

Hello Jerry, maybe there's a bit here to help you out. Best regards, Allan

Edit: sorry Jerry, the information that I was going to include is too large to be attached, if you have your email on your profile I'll send it to you directly. If you haven't included your email and would like this information please PM it to me and I'll send it to you. It's Miller's calibration information from their tech line.