The 488 GTE has a bug where the engine mixture number on the dash is 1 lower than it should be at all times. Here's a video that shows the issue, sorry for the low video quality. https://drive.google.com/file/d/1P4rfeczL8FUizz2_cxzjGoLBehZgt-un/view?usp=sharing
Probably a mix-up due to the un-conventional math used by ISI. All counting, in rF2 begins with the number zero. So 1 on a menu = 0 , 2 on a menu = 1 etc. The devs should have changed the onscreen display by one to make the wheel display match the text. It should be set so that 1 is the lowest viewable digit.
Un-conventional math, to use a base 0 developing programs? It's clear that they should convert the math to something human-friendly in the dash, but the normal math in development is the base 0 ones.
When you are taught to count from 1year old on, starting with 1, it can be confusing to non-math experts. So you are quite correct that sims probably all use the Base 0(I didn't even know what the term was) And yes...Quality Control testing should have caught the discrepancy.
The setup value can be set by the mod, so the best solution would be for the mod to define what gets shown on the dash and/or HUD.