OK, I am reposting this discussion. The first time I posted it there was some bad theory, which I will explain here. Regardless, in the mean time, dpaddock has provided a very good explanation with the obvious benefit of a lot of experience.
Standard atmospheric air pressure is 14.7 psi (appearing now, all over your dermis). Compressing atmosheiric pressure by a ratio of 7.25:1 renders 106.6 psi (a minor correction to dpaddock's number). So this was all well and good and makes sense on the gauge. Regardless, I wanted to see if there was anything I was missing in the compression pressure equation. Looking in Wikipedia, I found that the equation for calculating pressure includes an exponent to be applied to the compression ratio. The exponent represents the amount of additional pressure due to adiabatic heating of air (as in the heat that is generated to make diesel engines fire).
Solving the equation, 14.7 x (7.25 exp 1.4) psi = 235.4 psi. The exponent 1.4 being needed to allow for the specific heat of air. (I know I learned about all of this in Thermodynamics, but a lot has been forgotten). Wow, 235 psi! That was number I wasn't prepared for and which would never appear on a cyclinder pressure gauge. This was the point at which I removed the previous post. However, I believe I have figured out what the story is, but it is just my best guess. I think that the adiabatic heating process using the formula I've shown assumes that the change of pressure occurs instantaneously, or almost so. Kicking over the A10 is quite slow by comparison, so, it seems, there is not enough adiabatic heating to measurably change the pressure. So, the adiabatic heating does not mean much to us when measuring cyclinder pressure in a engine that is not running, but I think it is interesting because it probabaly does affect pressure in a running engine, particularly at high RPM. There would be quite a bit of power difference between 100 psi and 200 psi. I suppose this could be experimented with in a running car engine, but I haven't heard of it before.
I know this is tedious and long and seems like I am trying to teach physics, but I am just an audio engineer, as the name implies. Now, back to some other points from my original post. (dpaddock has explained this well from a different approach.) The 106.6 psi would be the gauge reading with absolutely no leakage. I would expect the reading to be slightly lower than this, even in a professionally built engine, as a little blow-by at the rings is inevitable. Also, the 7.25:1 ratio is probably not exact, as BSA wouldn't want to specify a compression ratio of something like 7.2342:1 (just a number I picked at random) if that was the actual, they would round it upwards. Another "also," air pressure where you are may not be, and probably isn't, exactly 14.7 psi, as it changes with weather and altitude. Yet another "also," 7.25:1 pistons would yield a different psi in over-bored barrels versus standard. You could go to a lot of trouble getting your actual atmospheric pressure and using that, but it probably is not worth it.
Now, more tidbits:
I usually kick over four or five times just to be sure I have a good reading. Hopefully, your gauge is of the type that holds the peak pressure reading. It does not continue to get greater with each kick after having reached its realistic reading. Why more than one kick is needed, I am not quite sure, it could be that it needs to get an even smear of oil on the cylinder walls.
If you get a low reading, you won't quite know the exact cause without further testing: If it's the rings, a shot of oil in the barrel will seal them better and, likely, lead to a higher reading. If no higher reading, then its the gasket or the valves. From here, I haven't done the tests to know what diagnostic approach to use. Maybe someone else can chime in explaining further.
Richard
