when to get them calibrated is a function of the frequency of use and how well they are treated. For many of us, they would never need to be re-calibrated 'cause we don't use them often enough or rough enough. On the other hand, if you're ISO certified, then there is a specific frequency when they must be tested and re-calibrated as necessary. Like my calipers at work...only need calibrated when some bozo uses them as a wrench or de-burrer.
Thanks for the reply wolf.Was just interested in how often for the civilian world. In the military and civil service world we had to do them every 90 days.That was for screwing ICBMs and nuc.s together.That led me to buy my beam types,so i can throw them around the garage. Thanks Jack