  CIPM published the Supplement I for GUM in 2008 as not only an alternative
approach to estimate the uncertainty for a given calibration measurement but
also as a proper uncertainty estimation one, whenever any of the conditions
imposed in GUM which must be satisfied does not hold [1, 2]. Before the
introduction of the new approach in the Supplement I, namely Monte Carlo (MC)
method, the GUM rules have been always applied even if in cases where the
mentioned conditions were not fulfilled. After or even before the official
introduction of this MC method, a number of published papers in uncertainty
estimation by using MC method had been shown up, giving more insight for the
ways the uncertainties estimated and also for the specific calibration
measurements under investigation themselves [3 - 16]. However, in most of those
published papers, the application conditions required before a method selection
should be analyzed, in fact, has been ignored. In our uncertainty study for
wavelength calibration by using beat frequency technique, the application
conditions have not been ignored but analyzed carefully and it was found that a
GUM application condition was unsatisfactory. However, all the MC method
conditions for this calibration problem have been well fulfilled. A computer
program was then coded [17] following the steps in the Supplement I. The
resultant outputs showed difference in statistical nature and suggested to
replace the MC method to the GUM one as soon as possible for this case.
