1970s, Advertisement, Photograph, Spirometer Spirometer, Monaghan M403, 1974, Advertisement April 26, 2014 Richard Johnston Leave a comment The Monaghan M403 used a hot-wire sensor. The readout was digital, the rest its electronic circuitry was likely analog. From: The British Journal of Anesthesia, 1974, Vol 46, No.2, Page 1.