Today, a technician from our local gas company (KeySpan, in New
England) came to our house to do some checking. He used a digital
natural gas detector to take some reading around the gas meter outside
the house. The reading varies from 0 to 0.20 (in 0.05 increments). He
didn't say there is any problem. Now I am curious what the unit is
(which I forgot to ask).

Doesn't anybody know what the unit is? Is it ppm? Can gas detector
detect 0.05ppm? Or the unit is something else?