I bought one of the no name compression testers about a year ago. A couple of weeks ago, I was testing the compression on my Dolkita 7901 and it showed only 130lb. I knew this was not right, so I tried again and noticed that the guage was leaking. So, after some research, I bought the Snap On MT308L compression tester kit. It is $199 new, but I got mine used on ebay for $75. What a difference. For good measure, I put a new schrader valve on it. This thing will last a lifetime. Just thought I'd share...