Ive got a half dozen various brand compression testers, every one reads different when compared on the same motor.
I don't think there's any standard of accuracy with these things.
When tested various saws I've got I get some that read high and others that won't read at all yet they run and cut fine.
My 90's 029 Farm Boss runs great, yet shows less than 50 psi on the gauge. My 036 which feels like its got very low compression
reads close to 160 psi, and my MS271 Farm Boss feels like its got too much compression in that the rope is severely hard to pull and hang on to, yet it reads only 120 psi. My vintage 032 reads 145.
I've got a Mac 10-10 which reads 180, and a half dozen old Homelite Auto 150 saws that read only 90 to 100 psi, yet all run and cut fine.
All of my comp. gauges are Snap On, Mac, Matco, OTC, and one Sears The one Snap on kit is a dedicated small engine kit with extra small hose ends to fit tiny engines.
My MS271 is so hard to pull I was concerned something was wrong with it when I first got it, it nearly rips your knuckles out just trying to hold onto the recoil handle. Yet it doesn't test very high on a gauge. Its got very little use and likely isn't even broken in yet. The dealer told me it'll get better with use.
It sits most of the time because I hate having to start it. I've actually strapped it down to my tailgate to start it it pulls so hard. I've got an older Husky 288 that's the same way.