As noted in the application note, the range of exposure times in the darkroom is very narrow - 4 seconds to 64 seconds is equivalent to changing the shutter speed on a camera from 1/4th to 1/60th of a second. NBD.
But unless you have some way of precisely measuring light and controlling exposure the whole reciprocity issue is moot.
For color you need to hold exposure time constant if you can.
When changing magnification the ((M + 1)/(m + 1))^2 formula works very, very well -- see the sticky thread at the top of this forum.
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