He devoted himself to mathematical study and was called, by Anthony à Wood, "the flower of mathematicians of his age"[3] John Blagrave was born as the second son to John Blagrave of Bullmarsh and Anne (daughter of Sir Anthony Hungerford of Down Ampney) in Berkshire at an unknown date sometime in the 1560s.

He was buried next to his mother at the Church of St. Lawrence in Reading, lying under a large monument to himself with a bust and several mathematically allegorical figures surrounding him (see portrait above).

The 'jewel' consisted of four movable parts - Mater, Rete, Label, and Rule - which were lavishly illustrated in the book's frontispiece and engraved plates.

The 'jewel's' uses were described in the third book as being used for anything from trigonometry, to navigation, to astrology; in Blagrave's words from the 'jewel' one could draw "so infinite a number of conclusions, more than I thinke I shall ever have time to write".

[18] Blagrave gave much to charity in his will, leaving a large sum of money to his servants and the local poor of Reading.

One of Blagrave's more eccentric charitable contributions was his lottery that awarded a sum of money to an unmarried Reading maidservant annually.