The publication resulted in a controversy, because another student of Oughtred's, Richard Delamain the elder, during the two years (1630-32) in which Forster was preparing the book, brought out two treatises on the same subject claiming the inventions as his own, and addressing himself to royal patronage.
Following the invention or discovery of logarithms by John Napier, in his Mirifici Logarithmorum Canonis Descriptio of 1614, the translation of that work by Edward Wright (1561-1615), and Henry Briggs's Arithmetica Logarithmica of 1624, the development of the slide rule had an important impact on the teaching of mathematics.
And this my restraint from such pleasing avocations, and holding him to the strictnesse of precept, brought forth this fruit, that in short time, even by his owne skill, he could not onely use any Instrument he should see, but also was able to delineate the like, and devise others: yet for all this my severe hand I saw him obliquely to glaunce his eye upon such Instrumentary practices: whereat I being jealous, lest I should lose my labour, and he his end, which was Art: I brake out into that admonition which in his Epistle Dedicatory to Sir Kenelme Digby he (I thinke in my very formall words) setteth downe.
Forster was strongly impressed, and told Oughtred he was surprised that he should have kept these valuable inventions hidden for "so many yeares", both from the world, and from himself, to whom his teacher had otherwise been so liberal in explaining the aspects and mysteries of his Art.
[5][7] This project (Forster also noted), while he was carefully working on it (1630-1632), "another to whom the Author in a loving confidence discovered this intent, using more hast then good speed, went about to preocupate [i.e., anticipate]; of which untimely birth, and preventing (if not circumventing) forwardnesse, I say no more: but advise the studious Reader, onely so farre to trust, as he shal be sure doth agree to truth and Art.
It was in an address To the courteous and benevolent Reader, prefixed to the two volumes bound together, that Delamain took the bait of criticism, writing:"Too great and too loose an aspertion hath bin cast upon me about these things, which I never thought in the least title when I first writ upon this Invention, or my name so to come to the worlds rumor as it hath since the last publication of this Logarythmall projection Circular; howsoever, here is my comfort, the guiltlesnesse and innocency of my cause, which may teach me, and others carefulnesse hereafter, how and what we publish to the world, seeing there are such carpers, and maligners even of the most usefull and best things, yea, such busie bodies who marre that which others make, who scorne to have a second, knowing all things and admiring nothing but themselves, such who have stings like Bees, and Arrowes alwayes ready to shoot against these whom they dislike, such who while they will needs have many callings neglect their owne; sharpe wittie cryticks, Diogenes like, snarling at others, and not looking home unto themselves, but by all meanes endevouring to take away the mantle of peace, and rent the seamelesse coate of love and amitie.
To speake ill of a man upon knowledge shewes want of Charity; but to raise a scandall upon a bare supposition, and to act it in Print, argueth little humanity, lesse Christianity..."[11]Oughtred responded at length in his Just Apologie (c. 1634), setting forth his own biography to show his precedence in the matter, and noting "Onely I will soberly tell you that William Forster, whom you call a Parrat speaking he cannot tell what, is a farre more grounded Artist in all parts of the Mathematicks then is R. D: and better knoweth what belongeth to demonstration then R. D. doth: as may soone bee tryed.
"[6] Following the dedicatory epistle to The Circles of Proportion was printed a short notice: "Thos that desire farther instructions in the use of thes Instruments or other parts of the Mathematiques may repaire to W Forster at the Red bull ouer against St Clements Church yard with out Temple bar"; from which it is inferred that he lived and taught mathematics there.