OldIHC

Jon, your results are why most mechanic's prefer a cyl leakage test over a compression test. There are too many variables with a compression test to gain much info. With a measured amount of air in and measureing how much leaks out, you can know the condition and even tell where it is leaking. Since the engine is stationary, cranking speed or throttle opening doesn't even enter into to it.
I'm not sure I even have a compression tester anymore. They can be ok for quick confirmation of something that you already suspect, but not good for much else.

agreed, but realistically most home garage guys don't have access to a leak down tester, so next best compression tester gives you a general condition report,

the instructions with mine said for a low cylinder add a little oil to see if it goes up, if not it's a valve or head gasket problem, my motor seems fine so I didn't do any added oil testing,

if I want to know condition of a running engine, I put a vacuum gauge on it,

Years ago, I modified my compression tester so it will adapt to shop air. I did this to hold a valve closed on a Ford 460 while I changed a lazy valve spring. I used this same modified compression tester adapted to a water column to verify a TDC on #1 cylinder on a Ford Flathead V8.

Thanks for doing that, BRJ. I always wanted to see those kinds of comparisons.
In the "repair shop environment" we are always in a race. Once the problem is isolated to non-ignition/ non-carburetion/ non-fuel injection/ non-vacuum leak, etc., I hopefully have a cylinder number to focus on. 1996 and newer OBDII will set a cylinder-specific misfire code. P0301, 302, etc. On 1995 and earlier vehicles misfire indication was NOT part of the computer's job. If the vehicle has a distributor then using a oscilloscope with a cylinder cancelling feature is nice.
The reason why I bring this all up is that you need to look at a poor running problem from as many directions as possible as quickly as possible (in my business).
And yes, the vacuum gauge should be one of the first tools out of the toolbox every time.
My customers are cheap. Any valvetrain involvement at all means stop instantly and refer to customer.
More often than not the diagnosis time is paid for and the vehicle is driven out as-is, often continuing to melt the catalyst. That's why the check engine light flashes on misfire, BTW.
Cool stuff! Thanks!
Someday I'll put my stock D-2 on emissions dyno and oscilloscope for all to see. I suspect very respectable emissions.