I'm struggling to add a sample sorry, but in simple terms if each worksheet (including the summary) was populated with 4 rows of data (called Data 1-4), with only one column of information (therefore my used range being A1:B4) and each value was £100, there were 4 worksheets (called Item 1-4) and each containing the same values, if in my other worksheet Items 1-4 were turned on then my total in the summary worksheet for each data would be £400, with a total ovetall of £1600.

So in the summary sheet, cell B1 I could add a formula like follows which would return the value of £400 for each data row).

=SUM('Item 1:Item 4'!B1)

However, if I turned item 4 off my summary worksheet should only show £300 for each data and £1200 in total.

If it is easier I would have a cell in each worksheet which would identify if the item was to be included in the summary calculations (A6 for example).

I could do this automatically by creating an input summary worksheet but I would need 44 (the number of items i.e. worksheets) * however many rows there are, I could then use an array formula to include or exclude the variance from there and sum all of the items from there.

However due to the volume of data I wanted to add a formula with this functionality into one cell in the summary worksheet.

Hope this helps, I have a fairly easy way to do this without much manual labour anyway but I prefer searching for better methods.