UHG..... when one starts to answer the drawing goes away...LOL

I don't think you need the pressure regulartor ( that will be on your air compressor anyway)... keep the guage which you have listed as optional ... and forget the one which is listed as going into the injector spot... otherwise you will be set up where you can't use your tool with normal gas engines...

When you put air in you will be looking at the guage and turning off the switch when it gets to the amount you want for the starting point...then time it as it goes down...

Air supply to cut off switch, to guage , to hole in system ( glowplug for diesel, spark plug for gas)

I think the percentage for valves compared to rings is determined by squirting oil onto the piston, thus sealing up the rings... the leak which continues from it is from the valves...

I have warned before that using TDC for putting air into the cylinder WITH OUT SOME MECHANICAL MEANS OF LOCKING THE ENGINE..... IS DANGEROUS.....

One cylinder of a 300 , when 100 psi is put on top of it is 1200 pounds of force... THE ENGINE WILL TURN IF NOT PERFECTLY CENTERED AT TDC....

This will probably mean you have to adjust the valves or the intermediate device so that the valves are shut at BDC... a real pain... and the reason that compression tests are more popular in my opinion... (popular but not more useful for diagnosing where your problem is)

Also I do not think that the amount of air which you can squeeze into a diesel at TDC will give you enough time to measure anything correctly...

You need some air compressed into the cylinder and then let it leak out... not enough total air if you have the piston at TDC....