Secretarial, or secretary shift is a shift lock mechanism in electronic keyboards that mimics the way that shift lock works on a manual typewriter. In typewriters, the shift keys physically shift the type basket, and pressing shift lock also locks the type basket into position. Releasing the type basket involves pressing shift.
Lock keys in electronic keyboards typically handle lock keys using either an indicator lamp or by way of an alternate action key. To reduce training costs when moving staff from manual typewriters to electric typewriters or terminals, some products were fitted with a mechanism that mimicked the mechanical shift lock of manual typewriters. Here, the shift lock keyswitch would be mechanically locked when pressed, and then released by either shift key.
Secretarial shift was offered by a number of electronic keyboard manufacturers. The following are listed in approximate date order.
No details on the Micro Switch SW Series implementation have been discovered; its existence is known from Product Brochure SW (373). The date of introduction is not known, but as SW Series was introduced around 1968, it is possible that Micro Switch had this design ready at this point. Secretarial shift (as secretary shift) was also offered with SD Series, introduced in 1975 or 1976, and likewise no details on the mechanism are known.
Clare-Pendar’s design is covered by US patent 3626120, filed in September 1970. A sliding plate held by a coil spring is pulled into a notch in the keystem of the shift lock key. A vertical bar is placed above each shift key, allowing the keycap itself to push on the bar and slide the plate aside, releasing the shift lock key.
Cherry supported secretarial shift with M6 series, and described their mechanism in US patent 3678255, filed June 1971 (although the switch shown in the patent is their reed switch type that has never been seen). Where Clare-Pendar used a coil spring, Cherry used a flat spring that rests against a keyswitch. The sliding plate of Clare-Pendar’s design is replaced with a rotating plate attached onto the shift key. This is one of the very few designs that has been observed; it can be seen in a B80-64AB keyboard of unknown purpose.
US patent 4071719—filed in July 1976—covers mechanical shift lock for one of the older series of Licon/Cortron ferrite core switches. ITW filed a later patent, in February 1980—US patent 4295012—covering the successor ferrite core switch series.
Marquardt’s “butterfly” switch series supported secretarial shift, and this was used in Olympia typewriters. No patent or documentation has been found for their mechanism.