Lee, you said "I'm curious about the method used by Bond, and the range of exposure lengths covered."

Howard's experiments covered up to 240 indicated seconds by factors of 2: 1,2,4,8 etc. He found the exposure for 400TX to be 1006 seconds at 240 indicated. This is about 1/2 stop less than I would calculate by fitting the whole range of data, but 1/2 stop is not much when you get down to it. I often find when I am metering a scene that I have to average readings with a greater spread than that, and even if I do three exposures at +/- 1/2 stop, I cannot see much difference in the final results.

If you find my article in Photo Techniques (sorry I don't remember the issue) you will see tables and graphs that illustrate what I am saying here.