0.5 to 1.0 sounds too low for the Gnat - we went supersonic during flying training, so a Machmeter with a 1.0 limit wouldn't have been much use. I can't remember exactly, but didn't we just have the OR946 combined ASI and Machmeter plus the 'precision ASI'? Or was that in the Bucc? Did we actually have a standalone Machmeter in the Gnat?