Very basic stuff I know but I can't get any sense from the Excel 'Help' pages - (as usual one gets a whole list of totally unrelated subjects!)

When I copy a formula from one cell into a number of others, sometime I want one of the functions to remail constant. In my old SuperCalc this was very simple as each time one copied a formula, when pasting, the option to keep any of the functions constant always cropped up. I've tried so many times to get an answer to this simple question but, as yet, have failed.

As a very simple example of what I mean: If I have a column of a number of months income from a number of enterprises and want the average per month I will divide the cell containing the first enterprize income by the cell containing the month number. To get the average for all the other enterprises I would copy the formula and paste in a column under the first answer but I want the cell containing the month number to remain constant. At the moment I would have to repeat the month number in a column for all the enterprises!

I'm sure there is a very simple solution but I can't find the answer anywhere!!