Hi Jeroen,
Thanks very much, that turned out to be exactly how it was done in the HSI I acquired today. The range dial was different, and instead of LED 7-segment displays was actually 3 dials on which 0-9 numerals were printed. These 3 dials were actually driven by 3 separate motors instead of a geneva wheel arrangement as pictured in my initial post - I'm not sure why this is the case, but perhaps when the aircraft is performing under significant G then this makes it more reliable.
Kind regards,
SBW