I've spotted some rather niche issues with the DISS-15 Doppler navigation controller which might be satisfying to fix!
The Lateral Deviation (БОКОВОЕ УКЛОНЕНИЕ КМ) and Distance (ПУТЬ КМ) displays are each dual roller-counter displays:
(OK, separately, in the English cockpit mod the labels are all misleading. They should be "LATERAL DEVIATION KM", "DISTANCE KM", and "COURSE ANGLE".)
The Lateral Deviation display looks like this when you're off course to the left:
And it looks like this when off course to the right:
However - the word "RIGHT" should appear on the other side, like this:
The display actually has six drums - three for "negative" (left-error) deviation and three for "positive" (right-error) deviation. "LEFT" and "RIGHT" are written a shutter that moves to hide the inapplicable drums as the aircraft passes 0KM deviation.
Exactly the same applies to the "Flight Path KM" / Distance KM / ПУТЬ КМ display and the "FORWARD" and "AFT" shutters.
You can see this kind of mechanism in this video at 13:00 - this is also a Doppler navigation control unit but I don't the guy knows this:
Note the "negative"/left/aft drums have the digits in the opposite order:
If you're wondering if I am a little bit obsessed with these roller-counters and with Doppler navigation instruments... you're absolutely right! I have a Doppler navigation computer in my living room, to a 1950s design - a generation older when it came to these roller-counter displays but the same general principle - two sets of drums and a shutter:
I made a working 3D model and simulation of this Doppler system and computer for X-Plane 10 back in the day. (I should complete that project.)
One other facet: I am 90% certain that, if you hold down the "Left", "Right", "Fwd", or "Aft" buttons, the motion should stop automatically on reaching 0 KM, and resume if you press the button again, based on the manuals for similar but older equipment in other aircraft. So, if you reach a waypoint showing 1.2 KM deviation to the right of track, if you press and hold "Left", and move your attention elsewhere, when you look back at the DISS-15 you'll see deviation steady at 0KM. Pressing "Left" again would resume the motion of the digits and show an increasing deviation to the left of track.
Benefits of simulating this display:
- clearer if you're left/right of track or before/after the waypoint based on a glance at which shutter is visible
- indicates to the user how these amazing mechanisms worked
- just looks cool
I love using the DISS-15, by the way. I've got its controls bound to HOTAS shortcuts, I use it that much. And I really appreciate the correct animation when a digit changes from 9 to 0 and drags the next drum along with it, e.g. when 39 changes to 40. So many sims get this wrong.