Now where can I get some of that?

This unit is one of 6 gas detectors we use on site if we're working in a potential flammable or explosive atmosphere area, before using them on site we "bump test" them which runs a gas through the unit to make sure its calibrated and alarms correctly otherwise it would just be a trinket hanging off our hips.
On start up it asks "fresh air calibration" which zeros the unit to ambient atmosphere but our site std is to use a calibrated gas to confirm the unit is in calibration too much waffle going on so time to get on the plant :-)