Calculation module

A calculation module for calculating the position of a mechanical element, the calculation module being operable to;

• receive an input signal,
• detect a plurality of corresponding features in the input signal,
• calculate the spacing between successive corresponding features,
• generate a numerical sequence in accordance with the spacing between successive corresponding features, and
• generate verification information associated with the numerical sequence to indicate possible errors in the numerical sequence.

An apparatus comprising, a movable mechanical element, a marking, a calculation module for calculating the position of a moveable element, the calculation module being operable to;

• receive an input signal,
• detect a first plurality of corresponding features in the input signal,
• calculate the spacing between successive features of the first plurality of corresponding features,
• generate a first numerical sequence in accordance with the spacing between successive features of the first plurality of corresponding features,
• detect a second plurality of corresponding features in the input signal,
• calculate the spacing between successive features of the second plurality of corresponding features, and
• generate a second numerical sequence in accordance with the spacing between successive features of the second plurality of corresponding features and a reader responsive to the marking to generate an input signal which is passed to the calculation module.

An apparatus comprising a movable mechanical element, a marking, a calculation module for calculating the position of a mechanical element, the calculation module being operable to;

• receive an input signal,
• detect a plurality of corresponding features in the input signal,
• calculate the spacing between successive corresponding features,
• generate a numerical sequence in accordance with the spacing between successive corresponding features, and
• generate verification information associated with the numerical sequence to indicate possible errors in the numerical sequence.
• and a reader responsive to the marking to generate an input signal which is passed to the calculation module.