Minimum 2 sensors are required for LCFMinimum 3 sensors are required for Notch Rejection (detection of notches on wafers which were not pre-aligned)Different systems may have a different number of sensors. However, all systems operate using the same fundamental principals:Calculated wafer center and make 1st correction leaving the SOURCE chamberCalculate wafer center and make 2nd correction arriving at the DESTINATION chamber.LCF must be calibrated per procedure when the tool is in production-ready stateLCF must be recalibrated per procedure when LCF sensors or Robot have been modified.