An optical measurement apparatus comprises an optical system (100) having a receiving axis (115). The optical system (100) comprises a source (102) that generates a probe beam that is directed to a location to be measured (114). A detector (112) of the optical system receives a reflected beam from the location to be measured (114). The apparatus also comprises a processing resource that receives an output signal from the detector (112) and makes an assessment of a characteristic of the output signal in order to determine a degree of alignment of the location to be measured (114) with the receiving axis (115) of the optical system (100).
