Excel doesn't handle sheet names that well. There are certain formulas you can use across sheets (e.g. like SUM(Monday:Sunday!D57) will sum up the values in cell D57 in all sheets from Monday through Sunday. But it won't auto increment sheet names like when you copy down or across in a sheet and it auto-increments rows/columns accordingly. Why don't you do the D57+D58 on each of the corresponding sheets? BTW another tip that can help is if you want the formula =D57+D58 to appear on all the sheets Monday-Sunday you can highlight all those sheets (shift-click on the tabs) and then type that formula in the cell you want on 1 sheet and it will be entered in that same cell on ALL the highlighted sheets. WARNING: as helpful and useful as this is it is also very easy to make a mess of things when you don't realize you have multiple tabs highlighted and start typing other things in so BE CAREFUL
