A diesel engine should be a lot higher than 200psi.
The compression pressure can be calulated from atmospheric pressure X the compression ratio of the engine.
Atmospheric pressure is 14.5psi and a diesel engine is typically 20:1 compression ratio.
Hence 14.5 x 20 = 290psi. You tend to end up with a lower pressure due to the rstrictionof the air intake.
Petrol engine testers are quite cheap, screw into the spark plug hole. I have a gunson one, cost about £17, only goes upto 200psi so won't do diesels. Also diesel ones need adapters to screw into the glow plug holes.
Last time I used it was on my daughters Fiat 500, got 75-140psi with engine runnng badly, 140-150 after head rebuild.
Thanks for that info... I can only unscrew 3 glowplugs as the 4th broke off the tip when I was trying to change it and the tip is still in there some 2 years later, just haven't got around to trying to extract it.