At Trinity my supervisor was J E Littlewood, perhaps the greatest pure mathematician of the time; but his supervision of undergraduates was rather superficial and I essentially chose the actual courses for myself.

... I was not impressed by the latter - possibly because there were too few students ... I also thought that the treatment was too theoretical; I suspect that Smart had never himself computed an orbit from three observations. I also attended Smart's course on practical astronomy at the Observatory, and duly determined its position with a sextant, an artificial horizon and 7-figure logarithms.

June 26, 1933. After Open Competition. Admiralty: Senior Assistant in the Nautical Almanac Office, Donald Harry Sadler.

I went for interview with D H Sadler very nervous as I couldn't find anyone even in my large department who knew anything about the Nautical Almanac Office. ... On arrival I realised that the Acting Superintendent was just as nervous as I was. (I found out subsequently he had just been appointed to that post himself.) The Offices were in the Royal Naval College, Greenwich. A magnificent building in which to work. We were allocated a few rooms in the College, D H Sadler in a room overlooking the river and the majority of staff in one large room ...

This volume, prepared under the joint sponsorship of the British Association and the International Astronomical Union, contains tables of Emden functions for $n = 1, 1.5, 2, ... 5$. These functions are solutions of a differential equation $D^2 y + \Large\frac 2 x\normalsize D y + y^ n = 0$ which is essential in the theoretical exploration of the internal constitution of the stars.

In the early 1930s posts for mathematical astronomers were few. Miller was clearly the best qualified and most suitable person to fill the vacancy of Assistant (later to be Deputy Superintendent) in H M Nautical Almanac Office. His illness, and its after effects, did not allow him to satisfy the Civil Service medical requirements either then or in 1934. This led to his leaving astronomy, and to my own appointment.

In September 1939 the Nautical Almanac Office was evacuated to Bath and the whole staff relationships changed. D H Sadler was suddenly responsible for all his very young and junior staff. He was instantly anxious and caring about us all and made certain that we were in suitable billets. I believe, despite the important work that the Nautical Almanac Office was called upon to do (D H Sadler seemed to put in endless hours), he was always concerned for his staff which increased enormously during this time. It can't have been easy for some one, who at that time appeared to live mainly for his work, to have in his charge girls whose fiancés and husbands were away fighting and who went through anxious times. He was most understanding and supportive. The day Bath was blitzed we all managed to get to the Office despite lack of transport except one, and I realised then just how much everyone was concerned for our missing member. D H Sadler turned up at last, very white and shaken, having dug himself and his elderly landlady out of the rubble - his concern was were we all there!

Unlike the other service ministries, the Admiralty already had a well equipped and knowledgeably staffed computing centre in the form of the Nautical Almanac Office. While before the war the Admiralty had sacked Comrie for taking on outside work, when war broke out the Admiralty recognised that it had an extremely valuable resource which it came under pressure to open up. Donald Sadler, Comrie's successor as Superintendent, began to take on outside work in autumn 1939. In the first two years of the war HM Nautical Almanac Office took on ballistics table work for the Ordnance Board, the Air Ministry and the Ministry of Aircraft Production as well as more specialist one off pieces of research work for various Admiralty research establishments; one example was a calculation involved in mine design. To add to the pressure on HM Nautical Almanac Office its own work had increased. Before the war the computation of star positions had been jointly shared between several countries. The war had terminated those agreements and HM Nautical Almanac Office had now to calculate all its own astronomical data for the annually published Nautical Almanac - now an even more critical publication for navigational purposes. However, it was not until July 1941 that Sadler received an extra member of staff to help cope with the ever increasing work load. Because of Sadler's unique position in running a major computing facility to which many service ministries were applying for help, he could see a need for a large, central computing facility to which all of the armed forces and the scientific civil service could have access. In 1941 he wrote a formal proposal for the creation of just such a facility but the suggestion came to nothing as the ever increasing crisis of computing resource had not yet been recognised by those in power. A suggestion from another quarter to centralise computing within the Admiralty did, however, bear fruit.

The Nautical Almanac Office moved from Bath to Herstmonceux Castle in 1949 to join other departments of the Royal Greenwich Observatory. Donald Sadler, the Superintendent, then carried through the unification of the almanacs of the UK and the USA. He and Gerald Clemence (Director of the Nautical Almanac Office in the US Naval Observatory) had to persuade the navies and the air forces to change their practices in order to arrive at a common content and format, and this was not easy. There was already a lot in common between the astronomical almanacs, but there had to be some give and take to get the final agreement on content and on the sharing of the work of computation and printing. Unfortunately, he could not persuade the Americans to change their title from 'American Ephemeris' to 'Astronomical Ephemeris (AE)'. The preparation of the 'Explanatory Supplement' was also shared, although it was only published in the UK. Sadler had been aiming even higher - for an 'International Astronomical Ephemeris', but he did not achieve this, although Germany gave up its 'Astronomisches Jahrbuch' and took over from us the work of publishing 'Apparent Places of Fundamental Stars'. The unification of the 'Nautical' and 'Air Almanacs' was accompanied by a unification of the auxiliary navigation tables and Sadler played a major role in this. He also designed the 'Star Almanac for Land Surveyors', which is still in use in its original form nearly 50 years later!

There was no prior announcement and the marriage came as a complete surprise to the current members of the staff. Flora continued to work, but after a short while she reduced her hours of attendance - probably so that she could devote more time to the preparations for the entertainment of guests at their frequent dinner parties. After a few years they moved from Flora's apartment to a new home in Cooden Beach. Many astronomers from overseas who visited the Royal Greenwich Observatory were entertained to dinner by them and they were also generous in extending their invitations to members of the staff and to some vacation students.

The Royal Institute of Navigation also owes much to Sadler's participation in its affairs; he was a member of the Steering Committee, the Preliminary Council and the first Council, which was elected in 1947 with (at Sadler's suggestion) the Astronomer Royal, Sir Harold Spencer Jones, as its President. He himself was President of the Institute from 1953 to 1955, and he was chairman of the Membership and Fellowship Committee for many years. He was awarded the Gold Medal of the Institute in 1957 and Honorary Membership in 1973. His presidential addresses to the Royal Institute of Navigation, and later the Royal Astronomical Society, covered the relationships between astronomy and navigation and the astronomical measurement of time. He continued to contribute to the 'Journal of Navigation' to the end of his life; his main interest was in astronavigation, but he also participated in the discussions on the rules for the avoidance of collision at sea and other aspects of navigation.

During the 11 years that I worked for him, mainly as his secretary, I never knew him to offer an angry word - just the odd grumble for a couple of months when he was told to stop smoking, but that soon passed and he soon reverted to his kindly self. He was always anxious to have Office outings and arranged for us to have several parties during our time in Bath. The bond that D H Sadler created between himself and his staff remained until his death, as was very obvious when old staff returned from near and far. I knew him as a kindly, courteous and modest man. Until I read his obituaries I hadn't realised just how much he had contributed to the world of astronomy and mathematics.

Sadler was a great competitor, and he took part in a variety of both outdoor and indoor sports and games. He was particularly keen on hockey and tennis, and he was also a useful cricketer and a member of the 'Royal Greenwich Observatory Stars' table-tennis team in the early years at Herstmonceux. He also enjoyed billiards, snooker and darts, and he won the Spencer Jones Indoor Sports Trophy in the Royal Greenwich Observatory Club in 1954; he used to organize a billiards match between the UK and the USA at International Astronomical Union General Assemblies. He was a good chess player, winning tournaments in town clubs as well as in the RGO, and he enjoyed bridge and any other game or puzzle that required skill or intellectual effort.

Although he made no major scientific discovery, Sadler contributed a great deal to astronomy and navigation, and it is probable that other fields of science have benefited from his diverse activities, particularly in the publication of mathematical tables. It must also be recognised that many young people gained valuable training and experience while working in the Nautical Almanac Office under his general supervision and that they have subsequently gone into other jobs in many different fields. Many other people have benefited from working with him in societies and international organisations, and those who came to know him as a friend will remember him with pleasure.

... remained at Cooden Beach for a few more years, but then returned to Aberdeen where she would be closer to her family. Her nieces have recorded how Flora had always been generous to her younger sister and to them and other members of the family. She had a bad fall in 1998 and had to move from her bungalow into a nursing home where she died on Christmas Day, 25 December 2000.