Designed and manufactured during the 1950s by Hermann Kolb Maschinenfabrik, Cologne, Germany, the company's OPCo "Optical" jig borer was available in at least four sizes with tables of 1200 x 600 mm, 1500 x 1200, 1750 x 1000 mm and 2500 x 1200 mm. Before the advent of digital readout systems (DROs) "optics" provided a similar degree of accuracy, but with - according to experienced users - some practise with the system and interpretation of measurements needed to get the best results. The pages below show the system used by Kolb 70 and how it was employed; the Kold 175 is shown here.