A metrology tool is arranged to measure a parameter of a substrate that has been provided with a pattern in a lithographic apparatus. The metrology tool includes a base frame, a substrate table constructed and arranged to hold the substrate, at least one sensor constructed and arranged to measure a parameter of the substrate, a displacement system to displace one of the substrate table and sensor with respect to the other one of the substrate table and sensor in at least a first direction, a first balance mass, and a first bearing which movably supports the first balance mass so as to be substantially free to translate in the opposite direction of the first direction in order to counteract a displacement of the one of the substrate table and sensor in the first direction.