1. A processor for determining centroid positions, executing: obtaining a corresponding baseline by each of a plurality of sensors when there is no touch or proximity of an external object; performing the following steps when there is a touch or proximity of the external object: obtaining a first touch related sensing information by subtracting the corresponding baseline from each value of a sensing information; obtaining at least one position; determining a corresponding first calculation range in the first touch related sensing information based on each position; determining a base value local to a touch or proximity of the external object based on the first calculation range, wherein the base value is the difference between the corresponding baseline and a signal of one sensor touched or approached by the external object or the difference between the corresponding baseline and a dual-differential signal of three sensors touched or approached by the external object; generating a set of calculation values by subtracting the same base value from all the values in the first calculation range; and calculating a centroid position based on the set of calculation values.