A rare George II set of gentleman's drawing instruments in a fitted

A rare George II set of gentleman's drawing instruments in a fitted, mounted shagreen case comprising: a pair of mounted steel dividers, another pair with swivel legs, an ink extension tool, a mounted ivory folding rule and an oblong scale rule and protractor combined, by Thomas Heath, London c.1740 both the protractor and folding rule signed "Thos. Heath Fecit" (lacking some fittings and top panel of case), the case 4.6in (11.5cm) high.