A measurement probe is described that includes a probe body, a stylus that is deflectable relative to the probe body, and a plurality of sensor elements for generating a sensor signal indicative of stylus deflection. An analyser is provided, optionally as part of a trigger unit, to analyse the sensor signals and issues a trigger signal to indicate the stylus has contacted an object. The analyser is arranged to combine a plurality of the sensor signals to generate a resultant deflection signal for comparison to a deflection threshold and is also arranged to detect oscillatory motion of the stylus by analysing at least one of the sensor signals. The analyser only issues a trigger signal when the resultant deflection signal crosses the deflection threshold and no oscillatory motion of the stylus is detected. The measurement probe may be used on a machine tool or other coordinate positioning apparatus.