Hi Team,
The Jigs we use have a calibration sticker on them indicating "Calibrated, ID#, By, Date and Due" We actually check these with a measuring tape and/or ruler to see if it's is in the specified tolerance. The question is, if the sticker says calibrated, is this politically correct?
Back here to the original question, you may want to obtain a copy of ISO 10012 for calibration guidance.
As others mentioned, the device used for either calibration or testing should be more accurate than the device being checked. Many use the 10:1 rule, partly because it is easy to move a decimal point. In many cases though, it is only 4:1.
So make sure the equipment is appropriate. A calibrated tape measure could easily be appropriate for checking your jigs, but a ruler to calibrate the tape measure may not be. You can buy calibrated tapes for around $40 to $45 so the expense of getting a properly calibrated tape really isn't much.
Make sure that the device has traceability to an international or national standard. If you calibrate it yourself, make sure your records show the device used and that the traceability trail is there.
On tape measures, as long as the tip isn't damaged and the numbers/lines are readable, a steel tape really does not go out of calibration. Buy a calibrated one, inspect it regularly, and replace it if the tip becomes damaged/bent or the numbers/lines become unreadable.
Calibrating tape measure has been a contentious topic here at the Cove, so I'm sure you will have many more comments about it.