The remarks of Mr. Harrison under the above title demand some further comment. One can certainly agree with his substitution of ‘prediction’ for ‘plotting’ but not with his deletion of ‘supposed’. The latter begs the whole question whether the operator will be dangerously deceived and this is far from proven. The latter part of his second paragraph is a generality; there will be many combinations of range and speed in which the result will not be satisfactory.

Mr. Harrison implies, although he does not come right out and say so, that errors arising during ‘classical’ manual plotting are ‘operationally’ acceptable while the errors in automatic plotting are unacceptable. Such a conclusion is illogical if one is willing to concede that any manual plotting procedure can be automated by the use of a digital computer. To examine this assertion in greater detail one may consider the automatic plotter to be made up of a data extraction section and a data processing section.