Their math is erroneous. They claim at, 300 dpi, a capacity of 300,000 analog images, per letter size sheet of Nanofiche, and at 600 dpi a capacity of 150,000 images. But the jump from 300 to 600 dpi requires four times (not two times) the capacity. So they probably can store only 75,000 images at 600 dpi.
Remember it's analog tech. Perhaps the 150dpi mode doesn't fully exploit the resolution of the material and the higher modes do?
I could imagine they would not want to make a single page too small (makes the readers more complex) so perhaps they draw the low-res images a bit bigger than needed.
