Abstract: A tyre condition monitoring system comprising a sensing unit adapted for approximation to a tyre to take a measurement of, or at least from which can be derived, tread depth, the sensing unit being adapted for deployment by manual approximation to a tyre and to store and/or transmit measurement data from one or more or all of a set of tyres on a vehicle as well as for mechanical approximation to a tyre for continuing and/or programmed measurement.