Ash you could have a look here http://www.scientificcollectables.com/index.html
W. Ottway & Co was established in 1640 at Orion Works, Ealing in London. They became well established opticians and by the late 1800s were manufacturing a wide range of different scientific instruments. According to Ottway's catalogue in 1899 they were manufacturers of; "Naval and Military Gunsighting, Telescopes, Theodolites, Tacheometers, Levels, Miners' Dials, Prismatic Compasses, Heliographs, Equatorials, Driving Clocks, Filar Micrometers, Coelostats, Transits, Mirrors, Flats, Naval, Military and Astronomical Telescopes, Prismatic Binoculars, Sextants, Auto Collimators, Star Image Collimators, Focometers, Clinometers, Clinometer Testing Instruments, Spectrometers, Spectroscopes, Ships' Electric Logs, Workshop Microscopes and Optical Measuring Tools, Brass Copper and Nickel Silver Mandrel Drawn Tubes."
What a great item to have from your step dad.