Patent ID: 7053392

Claim:
A method for making measurements of an object using an optical measuring apparatus having an output, which includes a light source which generates a beam of light, and a detector, upon which in use, and when the beam is not obscured, is incident the beam of light and which produces a signal dependent on the extent of the light incident at the detector, the method comprising: rotating the object; causing a beam of light to be emitted from the light source; moving the object relative to the beam; detecting the extent of the beam of light at the detector while the object is moved relative to the beam to determine the presence of the object; generating a signal from the detector when a predetermined extent of light is present at the detector; monitoring the occurrence of each signal from the detector; and causing an output to issue from the apparatus only if two monitored signals occur, a time interval between said two monitored signals being substantially equal to the time taken for the object to complete at least one rotation.