Compression readings are somewhat dependent on measuring conditions and technique. The screw-in gauges are best. Warm engine, fully charged battery, all plugs out, disconnect the coil primary lead so no sparks, block the throttle open about 1/4, and write down the readings as you go. If you can find the blue wire with its female spade connector behind the intake manifold on the firewall which allows you to use a remote starter, it's a one-person job. On my son's 81 B21F with 270k mi and a rebuilt head (stripped plug hole), 150-165psi; and on my daughter's 83 B23F, (145k mi) 180-195psi. Same gauge shows 125-135psi on my old MGB, so I believe it's fairly accurate.
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Bob (81-244GL B21F, 83-244DL B23F, 94-940Sedan B230F)