subtraction formula

Please excuse my ignorance. Up until January I had barely touched excel since 1998. My new position requires me to collect quite a bit of data; excel and I are becoming close friends.

I am creating a dash board which will allow us to look at various measurements related to chest pain patients. One of the measurements we look at is the time it takes for an ekg to be completed after triage. To get this data we simply subtract time ekg done from triage time. Not that big of a deal.

The problem is I have 150 patients from January in column A. I would rather not create an equation for each patient (for example c3-b3, c4-b4....). Is there a way for me to use a formula for an entire column that will subtract the difference between specified cells for all 150 patients so I don't have to type in formulas for each patient?

If you enter

=C3-B3 in one cell, you can just copy/drag that formula down the column and it will update automatically to reference the new rows.

to copy down, just select the cell the formula is currently in, click, hold and drag down the little black square at the bottom right corner of the cell, until you get to the end.

Even double-clicking that little black square might copy down the formula automatically if there is no blank column or rows to the immediate left.