The present invention provides in a first aspect an absolute shaft encoder to measure both the angular position of a shaft from a given radial axis and simultaneously or in sequence to record the number of completed rotations of the shaft passing through a given radial datum axis, the encoder consisting of a fist wheel and signal pick up means such that rotation of the wheel generates unique incremental signals defining the number of sectors of the wheel which have passed over a given radial datum position such that the radial position of the shaft can be recorded and displayed and actions initiated; at least a second wheel which, in use, provides further unique position signals from at least a further signal pick up means; an indexing mechanism to operate between the said first and second wheels and arranged such that each operation of the indexing device rotates the second wheel through an angle equal to the angle subtended by each sector at the wheel centre wherein, the first wheel is arranged to operate the indexing mechanism whereby for every completed turn of the first wheel the second wheel is indexed two or more times providing two or more position signals to the second wheel’s pick up device.