thought about that myself
I have always tuned my Oday 23 rig by feel, but I am sure that a real gauge would be better. I seem to recall that there were a number of posts previous on this topic. Try the archives. You can also try and see if Rudy at D and R Marine has some insight. If you are a regular here, you know Rudy's story (former manager at Oday, bought some of the molds, makes and sells Oday replacement parts, yada, yada, yada). His contact info is on this site in the links section.