Letters and cables regarding the Hartmann tests, including Redman's letter to R.F. Griffin at the Hale Observatory, 27 January 1972, concerning the mirror figure, the size of the Northern Hemisphere Observatory telescope, his travel plans, and observing on the Cambridge 36-inch telescope; and a copy of Redman's letter to S.C.B. Gascoigne, 27 January, referring to his time of arrival at Canberra, with a manuscript note regarding R.V. Willstrop's worry about a program error. There are also cables and letters sent by Willstrop to Redman in Canberra regarding possible errors; modifications to computer programs in the wake of the receipt of Redman's cabled message from D.S. Brown; and problems encountered, including the power crisis. Willstrop encloses with his letter of 17 February a calculation of the 6th power coefficient, part of a computer program, an explanation of the new program between labels 20 and 23, and a hand-coloured map of the errors supposed to be on the mirror.