The declinatory was used to assist in the accurate laying out of dials on walls or other plane surfaces, avoiding the need for calculation of angles by providing a precise template. Nicholas Bion (1652-1733) was "Ingénieur du Roi pour les instruments de mathématique", and one of the foremost instrument-makers of the period, but his instruments remain uncommon on the market. According to Maurice Dumas'S Scientific Instruments of the Seventeenth and Eighteenth Centuries and their Makers (London, 1972), "Together with that of Butterfield, the name of Nicholas Bion is most often quoted among contemporary instrument makers; yet despite this, very few examples of Bion's work have been preserved ... He does seem ... to have been a master of his craft with an excellent working technique. His workshop must have been one of the most frequented of his period. While his colleagues tended to specialize in the making of globes, mathematical instruments, sun-dials or mechanical devices, Bion was able to supply all these articles, whatever they might be, of excellent quality".
A similar example is described and illustrated as item 57 in Dirk Syndram Wissenschaftliche Instrumente und Sonnenuhren (Munich, 1989): "Nicholas Bion ... war neben Michael Butterfield der bedeutendste Hersteller von Sonnenuhren und wissenschaftlichen Instrumenten in Paris. Die Werkstatt, in der Bion seine ausgezeichneten Instrumente herstellte, war wohl nicht so großs wie die seines Konkurrenten Butterfield, so daßs die Produkte Bions weit weniger erhalten blieben"