US Patent 7440358 Visual indicating device

A visual indicating device comprising two or more discs (1, 2) each disc having a radial discontinuity (3, 4) to thereby form a surface of which the plane progresses in a helical manner, said discs being superposed and interleaved and lying in mutually parallel helical planes, each disc being independently rotatable about a common axis (5, 6) by drive means (20, 22, 30, 31) adapted to selectively rotate one (1) or other (2) of the discs, whereby the discs, when viewedaxially face on, display overlapping visually contrasting segments having an area or position representative of the relative positions of rotation of the discs and representing a value of a parameter to be displayed by the device.