Scan gauge will read actual transmission temperature. It is a very good way to read trans temp.
The factory gauge goes to the middle of normal once the trans gets warmer than 50F. It then goes to yellow at 230F, and red at 250F (I think - I could be off a little on this number.)
Former Ford Automatic Transmission Engineer
“The good thing about science is that it's true whether or not you believe in it.” ― Neil deGrasse Tyson