I never noticed it in the command room - I only remember the stock SH3 compass which had fixed degree markers on the inner part, and moving degree markers on the outer part. I wondered where OLC had had the 0-9 scale from - since he implemented it I thought it was for a reason, and didn't realise it came from an existing part of the boat in the game already.
Even if it was meant to be a vernier scale, the linear scale is far more useful anyway
Edit: The Medium Tanker is in the "NECT" folder as far as I can tell. Hope that helps!