This thread caught my fancy again. I looked around the shop for a Wixey angle gauge I last used about 10 years ago to measure accurate table saw blade angles. I had removed the lithium battery to extend its life, and it popped right into action when I inserted it. It calibrated almost instantly.
I checked ten new chains of different pitch and MFG and found them all to be within a half degree or so, from 5.8 to 6.2 degrees regardless of pitch. Then I checked several used chains. They ranged from 3.5 degrees to a whopping 12 degrees, the latter being the one that the saw swore at the last time I used it, even in cottonwood. I gave up on that chain and threw it away.
From now on, I intend to check this angle between the raker's top and the cutter edge after nearly every sharpening that I do. It seems far more accurate than the ruler depth gauge I've been using. It won't work on some so-called safety chains, but I never buy those.