I picked this up off ebabe for next to nothing. It's a copy of the Wellcome Photographic Exposure Guide - War Emergency Edition. I can't believe anyone actually used this.
To calculate an exposure, you have to look up a value for the film or plates being used...
...then look up a value for the light depending on the month, time of day and the weather...
...then dial the values into the calculator on the back page to get an exposure value...
...then you have to adjust it to suit different subjects, examples of which are given...
...by which time it's dark, your subject's disappeared and the war was probably over.