How do I make a reference to a cell such that it stays unchanged when I do a fill down? I have for example a sales tax amount reference in my formula, and when I fill down the reference to my sales tax cell is incremented too - I want it to stay fixed!
What you are looking for is called an Absolute reference.
To make an absolute reference you add a dollar sign on each vector of the address.
So, for an absolute reference to cell A1 - you'd write $A$1
Here is an example:
lets write a function for cell D1
Now, we fill down column D and the next formulas will be (for D2,D3,D4):
So, you see, the absolute reference doesn't change while the other ones fill correctly.