Mathematician and military engineer to Archduke Albert of Austria (1598-1621), Governor of the Netherlands, Coignet is known as a publisher, author, inventor, and scientific-instrument maker. In 1580, published an important treatise on the art of navigation (Nieuwe Onderwijsinghe, in French Instruction nouvelle ..., Antwerp, 1581), in which he presented a new method for determining longitude at sea by means of portable clocks. The volume also describes several newly invented instruments such as the nautical hemisphere. Coignet designed and built these instruments in the Antwerp workshop that he took over in the 1570s, in the footsteps of his father Gillis. Corresponded with Galileo Galilei (1564-1642) and became friends with the Salerno mathematician Fabrizio Mordente (1532-c. 1608), to whose proportional compasses he devoted several texts. Developed and described in manuscripts a number of refined instruments for proportional calculus: a proportional rule, called reigle platte (Traité des Sinus, 1610); flat-legged proportional compasses (De regulae pantometae, 1612); and four-point proportional compasses (El uso del compas proportional, 1618). In 1610, during the dispute with Galileo over the invention of proportional compasses, Giovanni Camillo Gloriosi named Coignet as the father of this popular mathematical instrument.