Watched a Youtube video - guy wanted to know compression in all cylinders. Has a system that only requires you pull one plug, and also monitor starter current. I assume you need a known-good cylinder. The one cylinder has a pressure transducer threaded into the spark plug hole. It measures starter current draw for each cylinder, based on the known good cylinder. Using an algorithm, using the know good cylinder pressure and current draw, it can calculate the compression ratio for the other cylinders.
https://youtu.be/hFs91VXnEHY?t=1052 (Compression testing starts @ 7:33 if times link doesn't work)
This guy is great to watch, his diagnostic skills are amazing.
Cool!
