fearofpavement
Trying them all
One thing to remember is that while a compression tester can be a useful part of diagnosis of the condition of a saw engine, low compression means you have a problem, high compression does not mean you don't have a problem. ie, I have had engines that had great looking pistons and cylinders that were worn out and produced low compression. I also have seen saws with badly scored pistons and cylinders that had great compression but were obviously not in good condition. Compression AND a visual inspection is important to determine the condition of the saw. When buying a used saw, it is not to be assumed that the seller is going to let someone "open" the engine of the saw to check it out. If the saw would be a bad deal if the engine has issues, then it probably isn't a good deal in the first place. If in doubt walk.
Regarding throttle open or closed, my position is it doesn't matter. Try it both ways and compare readings and draw your own conclusion.
Regarding throttle open or closed, my position is it doesn't matter. Try it both ways and compare readings and draw your own conclusion.
