B58-586 ROUTLEDGE ENGINEER'S RULE. I. Aston. Invented in 1811 and described by Phil Stanley as "probably the most elaborately marked and graduated boxwood rules ever made." A two fold, two foot rule with a brass slide and with extensive tables used to perform common engineering calculations of the nineteenth century. Marked "I. Aston Original Maker" and engraved "T.H. Campbell 1845" around the hinge. There were two Isaac Astons, based on the date this was the father. Very slightly sprung, but clean and very clear markings, hard to believe its 175 years old. Fine 300-600