The invention relates to a system for allocating service resources to users thereof, which service resources are intended to be provided at least one service point for service at one or more associated operator positions. There are two main embodiments of this reseller program. A first optical system includes a first light source to generate a first light beam which impinges on a surface of the substrate, and a first sensor to measure light reflected from the surface of the substrate to generate a measured first interference signal. Thus, the capacitance of the thin film coil can be reduced as much as possible.