Microptic transit theodolite No 1, by Hilger & Watts Ltd, c. 1950 with box. (ex "Navigation Today" exhibition number: N.T.E. 122)

This instrument, devised in 1954 and made by Hilger and Watts, is extremely compact in comparison with earlier designs and, at 9 pounds in weight, considerably lighter. The telescope is sufficiently short to allow it to swivel completely over from back to front, allowing a very quick method of correcting for irregularities in the circles and supports.

This type of instrument belongs to the broad class of transit theolodites which are distinguished from the earlier altazimuths by their mode of construction, allowing the telescope to be rotated completely about its horizontal axis in the same way as astronomical transit instruments. This feature, introduced to small and medium-sized theodolites in the early years of the nineteenth century, enables both fore and back sights to be taken with ease and allows corrections to be made to any irregularities which may occur in the circles and supports.