Calibration can fail if the Sense Input Gain is set too low (–45 dB) or too high (+20 dB). In the LCD setup menus, adjust Sense Input Gain for a proper gain setting. Check Sense for the current sense input level. The setting should be between -45 dB and +20 dB. You can also check the SENSE INPUT by listening with headphones connected to AMBIENT SENSE MONITOR on the front panel to hear what the 371 is reading.