Cell that retains value but adds to it if another cell is changed

Hello,

Just wondered if any of you guys can help.

I'm trying to get a Cell to hold the previous number in that cell and add to it if another cell changes. So I would like to have a cell with the heading 'Counted' and another with 'Total Count'. Every time the 'Counted' cell is changed i want it to add to the previous value in the 'Total Count' cell.

I have attached a little example to be a little clearer.

Any help would be much appreciated

Kind Regards
James