I read a thread a while ago showing a pressure gauge made to fit a Zodiac. There were 2 sizes of tubes and then a plastic stick glued in.
I made a similar contraption with a piece of hosepipe only. Around the gauge I rounded up some tape so the gauge has a snug fit. Then a bit more tape to thicken it up to fit the Zodiac plug. I cut a piece of the hosepipe off to leave a finger to open up the valve to take a pressure read.
Attached some photos of my gauge. Quite proud of my handiwork...
You might use a "No Mistake" steak meter as it uses pressure to move the gauge. Just measure with tube inflated to correct pressure and mark that point on the meter. Their cheap, simply mechanical in operation and ideal. Good luck.
