Cannon 6
Exactly. It is to make sure you chambered a round. You insert your mag, pull back on the slide and release, sling shot-ting the slide to load the round. The press check is just to make sure the slide peeled a round off of the mag. You ease back the slide till you can see brass in the chamber. It can be done a few ways.
1 is to take a GI model and loop your weak hand thumb in the trigger guard and use your weak hand trigger finger finger to pull back on the bottom of the slide.
2 is based on the thunder ranch principal of doing the same thing every time and they use the weak hand to make an inverted U and grab the slide pulling back to see brass. This same move is used to close the slide, clear stove pipes, and empty the firearm.
I like the thunder ranch idea as it keeps your weak hand away from the trigger and muzzle if you must press check.
The last way is the easiest! Drop the mag.
Is it missing a round?
Yes-it's loaded!
No, Try again.
I do not like press checks as they take the gun out of battery and it may not go back in. I think the same guy who invented shooting sideways on the TV invented the press check. Looks cool but helps the one your against be it clock or bad guy.