Reconstruction of Cluster Positions in the LHCb Velo

This note describes the `Velo Cluster Position Tool'. This software is used in the GAUDI framework to estimate the hit position of a particle traversing the silicon sensors of the LHCb VELO and to estimate the uncertainty on this position. This estimate and its uncertainty are used in the LHCb track fit. The definition of the cluster centre is given and the baseline linear approximation method presented. The position error is strongly dependent on the angle of incidence of the particle on the silicon sensors measured perpendicularly to the strips -- known as the projected angle -- and on the silicon sensor pitch at the point of incidence, and is parametrised in terms of these variables. Pull plots are presented to show the quality of the current tuning implemented for simulation events.