Why am I not surprised to find such thorough and thoughtful insight on such a niche APUG forum topic. There's a lot here that I need to still digest. It looks like making a test strip is probably the best bet, but at least the calculations will be useful to even get in the ballpark on the test strip. I find that sometimes I am way off base especially if proper exposure time goes from say 12s to 45s or so, the usual 3s test strip just isn't going to work at the longer exposure, so I will now know where to start with a certain base exposure.