This is the sixth of a series of articles presenting some thoughts about Le
ast Squares, Statistics, Quality Control and other related matters, which m
ay be of interest to students, or practitioners new to the particular appli
cations described. The treatment is deliberately elementary and the example
s are simplified so that the various concepts can be developed with clarity
. Now and then, the editor will enter a word of caution in the text, where
he feels that the treatment has been oversimplified or for other reasons. A
s in previous articles, the topic is presented as a dialogue between this p
ractising surveyor Nigel Atkinson and a retired academic Arthur Allan. The
editor encourages comments as the series unfolds.