This is an internal function that computes Grubbs' method of moments estimators of precision for the constant bias model using paired differences
A matrix or numeric data.frame consisting of an n (no. of items) by N (no. of methods) matrix of measuremnts. N must be >= 3 and n > N.
See Jaech 1985, Chapters 3 & 4, p. 144 in particular.
Estimated squared imprecision estimates (variances).
Richard A. Bilonick
Jaech, J. L. (1985) Statistical Analysis of Measurement Errors. New York: Wiley.