Cheapy china compression gauges are hit and miss, however the one l got from weedeaterman in a chainsaw toolkit he was selling about two years ago has been pretty good and accurate even though l don't trust it. l have a few cheapies and usually use two gauges when testing compression and untill l man up and get a snap on they are just a guide. l find the 'poor man's' compression tester works well and does not lie. Just hang on to the starter and feel how quick/slow the saw moves downward.