will instruct the user on when to apply zero and span gas.
The system will automatically adjust its internal settings to the proper calibration values without
further intervention by the user. Upon completion of a successful calibration, the system will
exit the calibration mode. Date stamp of last successful calibration will be retained in the
system internal memory, with capability to be shown on display. If calibration is unsuccessful
for any reason, the display must show an unsuccessful calibration attempt and revert to its
previous calibration settings. Use of flashlight type devices, magnets or clamp-on devices to
achieve calibration is not acceptable. The acceptable method uses a transmitter employing
a digitally encoded infrared light beam.