KEYBOARD HAVING VISIBLE AND INVISIBLE STATES

摘要

A chart recorder or other instrument has a window (10) within which is a key panel (1) composed of materials which are transparent in normal conditions. Incorporated in or associated with the individual elements of the key panel are display element (22) applied to the transparent window material (20). The display elements are normally transparent but become visible for example by fluorescence, when illuminated by radiation transmitted through the body of the transparent window material (20), rendering the key panel visible when needed for use.