the problem of depreciation would be a simple one, consisting of
spreading the value of the patent over its life. In addition to lapse
of time and operating simultaneously with it is the possibility of
supersession. Supersession as an element of depreciation is the attempt
to measure the probability of the patent’s being superseded before
the expiration of its term by a better machine, device, or method.
The measure of this element of depreciation is always speculative but
should be attempted with the best judgment possible.