Jacobus Valerius was based in Louvain and is known to have made astrolabes in the late 1550s. He probably worked in the workshop of Gemma Frisius and may have been related to Cornelius Valerius who became professor of mathematics and astronomy in Louvain after the death of Gemma Frisius in 1555.
E. Zinner, Deutsche und Niederl?ndische astronomische Instrumente des 11. bis 18. Jahrhunderts (2nd ed., Munich, 1967), p. 568; V. A. Rasquin, Dictionnaire des Constructeurs Belges d'Instruments Scientifiques (les origines ? 1914) (Brussels, 1996), p. 89.
Astrolabe, Attributed to Jacobus Valerius, Flemish, Dated 1558 (Oxford, MHS)