That's great -- you beat me to it!

But I think this will give you the ambient outside temperature and the charts reference TAT or total air temperature.  Essentially the outside air gets heated by friction on entering the engine resulting in higher temperatures as you speed up, which is TAT. The MS variable is TOTAL_AIR_TEMP .  You can calculate TAT if you know your speed and the outside temperature, but it's a lot of extra math.  Easier just to use a gauge showing TAT.