Keeping fixed cell reference in table

table 1 is a table of numbers
table 2 is a table of formulas to calcuate values based on table 1 and some constants.

the formula in the first cell in table 2 might look like:

=b21*0.28*2184/c4

My problem is this I want to copy this cell into all of table 2 without changing the reference to c4. In others words c4 will be in all cells like a fixed value. It wil not change to c5, c6 and so on.

How do i keep this absolute reference to c4 (i.e. keep it from changing as I copy the formula)?

I'm using excel 2003.

thanks