Flat Test Port Power Calibration and Linearity Calibrations are also Hardware Calibrations. From the front panel, an operator can start and abort these calibrations with ease. Usually there is a STOP or ABORT button. One can also send the GPIB command ‘ABORT’ to abort these manually initiated calibrations. However, when a calibration is initiated from the GPIB, the parser is busy waiting for the ‘Completed’ message from the internal interface and is not available to parse the ‘ABORT’ command to abort the calibration. Refer to the two sections above ‘Synchronization of GPIB commands’ and ‘Forcing the Parser to stop waiting’ to see how that is done. Once the parser is ready for a new command, send the ‘ABORT’ command.