Understanding Neutron Radiography Reading V-Kodak Part 2 of 3

Use Of Multiple Films
If the chart shows that the thickness range is too great for a single exposure
under any condition, it may be used to select two different exposures to cover
the range. Another technique is to load the cassette with two films of different
speed and expose them simultaneously, in which case the chart may be used
to select the exposure. The log relative exposure range for two films of
different speed, when used together in this manner, is the difference in log
exposure between the value at the low-density end of the faster film curve
and the high-density end of the slower film curve. Figure 47 shows that when
Films X and Y are used, the difference is 1.22, which is the difference
between 1.57 and 2.79. It is necessary that the films be close enough
together in speed so that their curves will have some "overlap" on the log E
axis.
Charlie Chong/ Fion Zhang
Radiography in Modern Industry. Rochester, NY: Eastman Kodak Co. 1980