In Glorious Multiplane - 3
So Bill Garity and Halley Wolfe applied for on July 31st, 1940 and were granted, on January 13th, 1942, a patent that pertains a device that can measure the light intensities on the artwork at a distance far enough away to be valuable, but close enough to allow for the layer above it without measuring its own shadow.
The patent mentions that the meter is easily movable to different parts of the drawing or title to be photographed. The fact that measurements are taken on a display away from the measuring device, connected by a wire, must have been a boon, too. Note that there are twelve claims to this patent, all confusingly alike for a non-engineer like myself! Well, it does mention that it also gives means for precise calibration and prevention of overloads, so that sounds practical enough.
Figure 2 shows clearly that this was designed for use on the Multiplane camera, also illustrated in the text where the example is given that the light intensity of a background that is further away from the camera should be appreciably greater than that of cels or drawings nearer the camera lens...