Abstract: A retrofit auto-indexing system for a turret punch press is described in which a predetermined location is provided to which both the upper and lower turrets of a non-indexing turret punch press are rotated. Upper and lower punching tools are mounted respectively in the upper and lower turrets in such a manner so as to be rotated simultaneously, using a single servomotor, to a desired angle. The auto-indexing system is controlled using a microcomputer which is connected to receive the numerical control programmed data, determine whether the code it is receiving relates to the auto-indexing function and, when it does, institute the instructed auto-indexing function. Otherwise, the microcomputer passes the numerical control programmed data directly to a minicomputer which operates the turret punch press in a known manner.

Abstract: An optical fibre capable of monomode transmission in, and having a wavelength of zero dispersion in, the 1.55 .mu.m window and having a core comprising silica and germanium dioxide and a cladding comprising silica is drawn from an appropriate preform at a temperature in the range from 1900.degree. C. to 2000.degree. C. Fibres thus produced have low loss compared with fibres drawn at higher temperature.