Why NOT retain test results. It takes about 10 minutes per week to downlaod them. If you use a tester with PC link & software it automatically saves the data on the PC in any case.

If something goes seriously wrong with a piece of kit and you get asked to provide maintenance records then you will be bound to be asked "Where are the test results then ?"

As for spending time analysing drift in values I've never met an engineer who did that. If the unit passes you get on with the next task. If it fails you fix the problem re-test then retain a before and after result.

If you get audited the question always asked is "Where's the evidence ?" If you chucked away your test results where's the evidence you ever did the tests?

Also if you've trained a new technician and passed them to work unsupervised it's very usefull to be able to check their test results for the first couple of months just to be absolutely sure they are running the tests correctly and don't need help.

Marc