downfeed apparatus in a grinder controlling the grinding wheel down in fast , medium and slow speeds , and up in fast speed . it is fed down continuously in successive passes throughout the grinding operation , and at the end of the grinding , the grinding wheel continues through a spark - out mode at a constant level . a previous control program is held in a memory for later use in an identical operation on an identical workpiece . a monitor presents all steps taken in every mode and every step , and shows progress of movements enabling the operator to manually set and adjust the control apparatus simply and accurately by watching the monitor while making the adjustments . the monitor also continuously presents all movements in an automatic operation .