MikeW wrote:Totally irrelevant.
It's barometric. Pressure transducer.
Aha. Yes, so I see. I was thinking of something totally different, weekend memory strikes again . Still a point worth making though for others, given the increasing amount of airspace infringement reports where a GPS log is used as proof of altitude, much as with a low flying issue I consulted on last year elsewhere in the world, where a regulator tried to use a GPS log as proof of negligence.
Modern barometric transducers a much better way than an ageing mechanical system !