Patent ID: 7821420

Claim:
A transmission system for a measurement device for a coordinate positioning apparatus, comprising: a measurement device comprising a touch trigger probe; a first station for mounting with the measurement device; and a second station for mounting with the coordinate positioning apparatus, wherein the first and second stations communicate using a spread spectrum radio link, the spread spectrum radio link being a frequency hopping radio link in which the first and second stations frequency hop between a series of different frequency channels, in the event of a measurement event comprising a trigger event, the first station transmits information relating to the trigger event, including data relating to a time of the trigger event, when a signal transmitted by the first station containing information relating to the trigger event is received by the second station, the second station produces a measurement device output signal, with a time delay between the trigger event and the production of the measurement device output signal, when the signal transmitted by the first station is not adequately received by the second station, the signal is retransmitted by the first station, the time delay being sufficiently long to allow the first station to retransmit the signal within the time delay, the first station comprises a timer for measuring a time between the trigger event and the transmission of the signal comprising information relating to the trigger event, the information relating to the trigger event including the time measured by the timer, the retransmitted signal comprises updated data relating to the time of the trigger event, and the delay between each trigger event and a resulting machine station probe output is substantially constant.