A metrological instrument for determining a surface profile of a surface of a component, the instrument comprising: a component support for supporting a component; moving means for effecting relative movement between a measurement probe and the component support so that the measurement probe follows changes in the surface in a direction perpendicular to the relative movement direction; measurement means for providing measurement data indicating the displacement of the measurement probe as the measurement probe follows the changes in the surface; orientation control means for controlling the orientation of the component; measurement control means for controlling the moving means to cause the measurement probe to follow a reference measurement path (61 c) with the component in a first orientation so that the measurement means obtains reference data, the measurement probe to follow a first section (61 d) of a measurement path along the surface with the component in a second orientation so that the measurement means obtains first measurement data, and the measurement probe to follow a second section (61 e) of the measurement path along the surface with the component in a third orientation so that the measurement means obtains second measurement data; and processing means for processing the measurement data, the processing means being operable: to define a datum using the reference data, to align the first measurement data to the datum to produce aligned first measurement data, to align the second measurement data to the datum to produce aligned second measurement data, and then to use the aligned first and second measurement data to generate a surface profile of the surface of the component. a component support for supporting a component; moving means for effecting relative movement between a measurement probe and the component support so that the measurement probe follows changes in the surface in a direction perpendicular to the relative movement direction; measurement means for providing measurement data indicating the displacement of the measurement probe as the measurement probe follows the changes in the surface; orientation control means for controlling the orientation of the component; measurement control means for controlling the moving means to cause the measurement probe to follow a reference measurement path (61 c) with the component in a first orientation so that the measurement means obtains reference data, the measurement probe to follow a first section (61 d) of a measurement path along the surface with the component in a second orientation so that the measurement means obtains first measurement data, and the measurement probe to follow a second section (61 e) of the measurement path along the surface with the component in a third orientation so that the measurement means obtains second measurement data; and processing means for processing the measurement data, the processing means being operable: to define a datum using the reference data, to align the first measurement data to the datum to produce aligned first measurement data, to align the second measurement data to the datum to produce aligned second measurement data, and then to use the aligned first and second measurement data to generate a surface profile of the surface of the component. to define a datum using the reference data, to align the first measurement data to the datum to produce aligned first measurement data, to align the second measurement data to the datum to produce aligned second measurement data, and then to use the aligned first and second measurement data to generate a surface profile of the surface of the component.