I have it vertical and off the bike , however I did not remove the springs.. It wasn't necessary. I have reassembled it and am now trying to figure out how much oil is in there. I have added about .75 liters but can't measure the oil depth.
Have I missunderstood when he said to compress the shock?

You're fine. The way I measured mine was to snag an 8" long 'zip tie' off the work bench and use it as a dipstick. It is thin enough to fit down the vent holes and the spring and such. The ridges on the back also are handy for reading the oil level. I put in just shy of the recommended amount and then checked with the dipstick. Then added until it was right.
Gryphon