This is trivial but I'm just curious just how you do it? If low, then how do you go about adding the proper amount? What kind of fluid - concentrated, 50/50 mix, what kind? Where do you get your fluid?
Honestly i dont know the "by the book method", and i have never had to add any but if i just had to add a little bit i would just use 100% coolant. If i had to add a large amount i would mix 50/50. Or in a perfect world i would just buy the premixed stuff and add that!!!!!!!!! AS for checking the level, i just use the vertical seem in the tank, that where it was new and where it still is!!!
Dex-Cool is the proper coolant. It is pre-mixed, so additions are easy. There are several brand names, but what you use must say "silicate-free" on the jug and be pink. Do not use green stuff. When the engine is cold, remove the coolant expansion tank cap (only one BTW) and fill until the coolant level is at the seam in the tank(1/2 full).