[10] Admitted to holy orders, he left the University of Cambridge about 1603, when as "Master" William Oughtred he held the rectorate of St Mary's Church, Guildford, Surrey.

[11] At the presentation of the lay patron George Austen, gent., he was instituted as vicar at Shalford near Wonersh, in the neighbourhood of Guildford in western Surrey, on 2 July 1605.

[19][20] Elizabeth's brother Gerald, 2nd Baron Aungier of Longford, was married to Jane, daughter of Sir Edward Onslow of Knowle, Surrey in 1638.

Oughtred praised Gerald (whom he taught) as a man of great piety and learning, skilled in Latin, Greek, Hebrew and other oriental languages.

Oughtred was presented by Sir Edward Randyll of Chilworth (lord of the manor) to the rectory of Albury, near Guildford in Surrey and instituted on 16 October 1610,[24] vacating Shalford on 18 January 1611.

[30] The Park and landscapes,[31] which formed the subject of a series of etchings produced by Wenceslas Hollar, c. 1645,[32] were developed in this period, before a parliamentary sequestration which was eventually discharged in 1653.

[33] William Lilly, that celebrated astrologer, knew Oughtred and claimed in his autobiography to have intervened on his behalf to prevent his ejection from his living by Parliament in 1646:"About this time, the most famous mathematician of all Europe, Mr. William Oughtred, parson of Aldbury in Surry, was in danger of sequestration by the Committee of or for plundered ministers; (Ambo-dexters they were;)[34] several inconsiderable articles were deposed and sworn against him, material enough to have sequestered him, but that, upon his day of hearing, I applied myself to Sir Bolstrode Whitlock, and all my own old friends, who in such numbers appeared in his behalf, that though the chairman and many other Presbyterian members were stiff against him, yet he was cleared by the major number.

"[35] Of his portrait (aged 73, 1646) engraved by Wenceslas Hollar, prefixed to the Clavis Mathematica, John Evelyn remarked that it "extreamly resembles him", and that it showed "that calm and placid Composure, which seemed to proceed from, and be the result of some happy ἕυρησις and Invention".

Among the short tracts added to the 1647/48 editions of the Clavis Mathematica was one describing a natural and easy way of delineating sun-dials upon any surface, however positioned, which the author states he invented in his 23rd year (1597/98), which is to say, during his fellowship at King's College, Cambridge.

"[2] This projection answered his search, but then he had to invent theorems, problems and methods to calculate sections and intersections of large circles, which he could not find by instruments, not having access to any of sufficient size.

In London, in spring 1618, Oughtred visited his friend Henry Briggs at Gresham College, and was introduced to Edmund Gunter, Reader in Astronomy, then occupying Dr Brooks's rooms.

Delamain, who being conscious to himself that he is but the pickpurse of another man's wit, would thus inconsiderately provoke and awake a sleeping lion..."[41] Around 1628 he was appointed by the Earl of Arundel to instruct his son William Howard in mathematics.

[43] In 1634 he corresponded with the French architect François Derand, and (among others) with Sir Charles Cavendish (1635), Johannes Banfi Hunyades (1637), William Gascoigne (1640)[44] and Dr John Twysden, M.D.

[45] Oughtred offered free mathematical tuition to pupils, among them Richard Delamain and Jonas Moore, and his teaching influenced a generation of mathematicians.

Seth Ward resided with Oughtred for six months to learn contemporary mathematics, and the physician Charles Scarborough also stayed at Albury: John Wallis and Christopher Wren corresponded with him.

[48] The first edition of John Wallis's foundational text on infinitesimal calculus, Arithmetica Infinitorum (1656), carries a long letter of dedication to William Oughtred.

In the English Foreword, Oughtred explains that the intention had always been to provide the ingenious reader with an Ariadne's thread through the intricate labyrinth of these studies, but that his earlier, highly compressed style had been found difficult by some, and was now further elucidated.

[54] These editions contained additional tracts on the resolution of adfected equations proposed in numbers, and other materials necessary for the use of decimal parts and logarithms, as well as his work on delineating sundials.

Forster, who dedicated The Circles of Proportion to the famous intellectual Sir Kenelm Digby, observed that another person had hastily anticipated Oughtred's publication.

[66] Trigonometria, Hoc est, Modus Computandi Triangulorum Latera & Angulos was a collection compiled from Oughtred's papers by Richard Stokes and Arthur Haughton.

[8] It carries a frontispiece portrait of Oughtred similar to that by Wenceslas Hollar, but re-engraved by William Faithorne, and depicted as aged 83, and with a short epigram by "R.S."

was added to a 1653 edition (in English translation) of the pioneer book on recreational mathematics, Récréations Mathématiques (1624) by Hendrik van Etten, a pseudonym of Jean Leurechon.

[76] The Hermetic science remained a philosophical touchstone among many reputable scientists of his time, and his student Thomas Henshaw copied a Diary and "Practike" given to him by his teacher.

Oughtred penned an approving testimonial, dated 16 October 1659, to the foot of the English abstract of The Cabal of the Twelve Houses Astrological by "Morinus" (Jean-Baptiste Morin) which George Wharton inserted in his Almanac for 1659.

Among other discourse, he told me he thought water to be the philosopher's first matter, and that he was well persuaded of the possibility of their elixir; he believed the sun to be a material fire, the moon a continent, as appears by the late selenographers; he had strong apprehensions of some significant event to happen the following year, from the calculation of difference with the diluvian period; and added that it might possibly be to convert the Jews by our Saviour's visible appearance, or to judge the world; and therefore, his word was, Parate in occursum;[88] he said Original Sin was not met with in the Greek Fathers, yet he believed the thing; this was from some discourse on Dr. Taylor's late book, which I had lent him.