In FTIR providing interferometer techniqe ,it is
mathamatical operation by in which possible scanning done
40 times in one minutes and give better resolution . It is
calibrated by using Polystyrene film ( MIR flim ) 0.38 mm
for wave number , Resolution & noise test etc.
FTIR interferometer techniques by which it scans 50 times
in a minute, providing better resolution.
It is internally calibrated by He-Ne laser.
Digitally it can be subtracted or can make addition,
But it is costly.