In the Wafer Mapping System on the ASPEN II, the cylinder is connected to the potentiometer and that makes the door travel up and down. The change of resistance value in the potentiometer can decide the position of wafer sensor and operate wafer mapping. The potentiometer is a device that changes resistance value followed by mechanical tangency. When it is used for long time, the tangency would wear away and it would affect errors in resistance value. Also, outside environment (temperature, humidity) can cause errors in resistance value. These problems are causing mapping errors. BCGTech, Inc. has developed a mapping controller called the CMTA-II, which resolves these problems for the wafer mapping system for the ASPEN II. The CMTA-II offers the one and only solution that does not affect performance on ASPEN-II, with a minimum change of equipment elements and minimum cost to upgrade the mapping system. The CMTA-II provides IBM compatible capacity that connects to the PC and provides constant monitoring for mapping status. This leads to greater efficiency and accuracy of the mapping system.