Out Of The Blue Artifacts A Library of a lifetime of collecting
Metric Methane Calculator.
National Coal Board N.C.B. Metric Methane Calculator.
Made from Plastic and Brass with a P.V.C wallet. Size 6″ inches diameter.
It has 4 revolving calculating discs on the front and 1 on the back.
National Coal Board N.C.B. Metric Methane Calculator