Plug in the block heater and get at least *some* heat in the block. Hook the engine up to two batteries if possible, or use heavy (2-gauge) jumper cables to a running vehicle - you'll need lots of power for all the cranking you'll be doing. Crank each cylinder until the gauge stops increasing, usually at least 6-8 compression strokes, maybe more with a cold engine. Repeat the test a second time on all 6 cylinders, average the results.
While the raw numbers will be mostly irrelevant when cold, you're looking for equal pressure between cylinders, within 3 bar from highest to lowest. I would definitely try to get the engine running so it can be hot for the test. Even cold, though, it should be well over 20 bar (spec is 26-32 bar hot).
