Zeiss horizontal optimeter, 1939 with stand, lamp and projection unit and mirror and prism.

Zeiss developed a reputation for the highest attainable standards in optical and metrological equipment. The horizontal optimeter was first exhibited at the 1920 Leipzig Fair (this particular example dates from 1939); it soon became one of the most useful and widely-employed instruments in engineering standards rooms for gauge inspection and control – in this sense, the optimeter was the arbiter against which many other items of metrological equipment were checked.

During the inter-war period, Britain relied heavily on Zeiss instruments like this one. When World War Two broke out, the UK was placed at a severe disadvantage as the supply of instruments from Germany ceased while demand for them in armaments production had never been higher. A result of this was the introduction in the UK of ‘BTZ’ instruments, examples of which we also have in the Industrial Metrology collection. These were pirated copies of Zeiss machines, ‘BTZ’ standing for ‘Better Than Zeiss’.