Reeve, C.; Veale, R.
NBS Internal Report 73-232; 25p. June 1973. Keywords:
Calibration; optical flat; profile; stability; standard deviation. Abstract:
Some optical flat owners are concerned about the long term stability of their optical flats. To examine this problem, a survey was made of several optical flats which where calibrated by the National Bureau of Standards at least three times during the period from 1959 to 1972. The measured profiles of these flats are presented graphically so that the different calibrations can be compared. The conclusion of this survey is that optical flats are quite stable over a period of several years, but since the individual requirements for precision may vary greatly, it should be left up to the owner to weigh the appropriate factors in determining how frequently he needs his optical flat calibrated. | 
