I have been pretty deep down the rabbit hole here. I went to good old you tube for help measuring pressure angles. I found nothing useful in the home shop in English. Hindi, yes. English, no. Makes a guy a bit more worried about how far my country has come and what direction we're headed. I eventually found something usable via google. Not a direct method mind you, but thankfully there are only two main suspects for pressure angles. That means probably only running the math twice if the first guess was wrong. What I found was formulae that involved dp. So the first step, divide 25.4mm by module 1.5. I get a DP of 16.933333. Now I take the cosign of my first guess of 20degree pressure angle(.9396926) and multiply by Pi, giving me 2.9521314. I divide this by the DP of 16.933333 and get .1743385. I add this to the number measured in inches(.4675) over 3 gear teeth ( as in squeeze them with my calipers). This gives me .6418385 for an answer that should represent the measurement over 4 teeth. The measurement I took was .6405" over 4 teeth. That's incredibly close to right. Should that have come out way off I would have done the same math but with the cosign for 14.5degrees. I would say this exercise left me feeling pretty confident of both module and pressure angle. Also a little sore in the noggin. So off to bang good for tools I can justify spending $ on. Hopefully someone else can use the math. I know I'm not the only one to want these answers before spending money.