Range finder question???

[TMT]

I am confused about range finders and the "TBR", "ARC", or "ID" option.  Hopefully someone can help me out.
Do you enter in certain parameters, such as elavation, bullet weight, speed, etc..?
Or do they use some sort of nominal values? 
I understand the gravity aspect of the equation, but without knowing the other variables how accurate could it be?

[Sew Sille]

I have a bushnell 1500 arc. I can set it to my 300 wby mag with the bullet weight and if you range somethind up or down it will tell you 350 yards, but to like it is 310 yards or what ever it should be. It is a neet tool.

[The General]

I just purchased a new Nikon a few weeks ago.  According to what i've read and asked people at Cabelas, Scheels, and Gander they all recommended the Nikon.  Every onw als said unless you are making long shots up or down a mountain the ARC is not needed.