That's a very good point, actually. The traditional 35mm film format is 24 x 36mm in dimensions. I was assuming Poser used that, and it fit well enough when I compared the outcome to Lux, which according to the documentation uses 32mm as the film height.

But: I saw a slight discrepancy that I couldn't quite explain. If instead of 24 x 36mm, the Poser programmers had used 1 x 1.5in, that would get us very close to the value you measured (half an inch is 12.7 millimeters). I'll check that tomorrow. Obviously, I could have done some more exhaustive measurements right away, but for today I was content getting an approximation.

-- I'm not mad at you, just Westphalian.