This is a question I have to admit I don't know the answer to, hard to believe I know! What is the period after which test equipment needs re- calibrating? As far as I know it is yearly, but I could be wrong. I ask because the dno I worked for had an engineer who built a test rig. The idea was that as there were about a thousand items of test gear used at our depot, it would be more economical to do it in house. So every year a dedicated set of test instruments were sent off to be calibrated. They were then used as 'masters' to be compared to via the test rig. Some items weren't tested, such as pulse echos, sniffers, cat and Genny etc, which either worked or didn't, same with Fusemate and Rezap portable circuit breakers. We were able to test AC and DC current and voltage earth / neutral loop impedance, impedance and afew other tests like phase rotation, test lamps etc. What do others think of this method? Any items found to be outside the limits were sent away for recallibration or scrapped. I think the only test gear not tested was the RCD tester, which we didn't use anyway. I would like to hear opinions on this, for once it doesn't concern me!