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When photomultipliers are used, the spectral response depends in a complicated
way (involving several different phenomena) on the electrode potentials in the
first few stages.
If the high voltage is changed to vary the gain, as is sometimes done in DC or
CI work, the spectral response varies.
This must be treated exactly like a variable measuring aperture: only data
taken under constant conditions should be reduced together, but sometimes
this can be done if adequate calibration data have been measured.
The column label is PMTVOLTS.
Once again, because several complex effects are involved, the effects are not
predictable, so there is no point in trying to use quantitative values.
Besides, the voltage settings on many power supplies are not very accurate, nor
can one read an analog voltmeter precisely enough to obtain useful numbers.
The values in this column will be treated as strings rather than converted to