Okay, so if we say that you put solution A in the burette and add it to solution B (which is probably in a conical flask or something similar):
Well the range finder is just a practice titration. So you do it roughly and if you ended up using 25.50 of A to neutralise B, you know that the volume of the liquid ACTUALLY needed to neutralise B is going to be just under 25.50, so you know what kind of value to expect when you do more accurate titrations.
If you also know what A and B are called, you can write out an equation. When you balance it, you can see how many moles you will expect to use in this reaction.
For example, if the equation shows that you need 2 moles of A to react with 1 mole of B, and you are told to use 10.00cm^3 of B, then you will expect to add ABOUT 20.00cm^3 of A to it.
I hope this makes sense... I haven't done a titration for ages, so my knowledge is very hazy...
