How noses are calibrated

The company I work for actually helps people calibrate their sense of smell! In case you're wondering if this is a wind-up, let me explain : in the gas industry, the gas doesn't smell until an odorant is added. The best piece of equipment for testing if the right amount of odorant has been added is still the human nose - until a 'better' alternative is developed. And like all equipment, even the human nose needs calibrating for this work. The BBC recently featured the labs where this happens.