Overfilling is as bad as underfilling, you can blow all the seals and render the engine useless. Tbh you really need to read the level off the dipstick, I appreciate it's not that easy but neither is it impossible. Read from both sides, wipe in-between dipping and only read after the car has been sat still for 10-15 mins on a level surface.
You're taking a hell of a chance reading using the pressure gauge alone. I'll admit to doing so on my old car, however that was in conjunction with reading off the dipstick and knowing how pressure equated to levels on my particular engine: It'll be different between cars.