Ive never in over 10 years of ribbing checked the pressure with any guage, I usually just check with my hand checking they are not soft, firm but not overly hard, the weather temp will effect them very much, a cold day in winter they will go soft, in summer they may appear slightly soft first thing in morning but as temp rises will harden up, if they feel right they are right in my opinion.
Generally 0.20 or 0.25 bar (2.9 or 3.6psi)
Many have pressure indicated on transom plate.
We use a gauge and keep tubes at recommended pressure of 0.2 bar. In my opinion there is much more stress on tube joints if run under inflated, and you see many ribs out there with soft tubes.
