I have twelve worksheets (one for each month of the year). On them are
customers and expenditure figures. Each sheet has some customers repeated and
also some different ones. I want a thirteenth sheet that lists all the
different customers from the year and shows their total expenditure for the
year. I can then add some graphs and sort the accumulative data into 'top
ten' and 'worst ten' customers etc.

How do I create this thirteenth sheet with minimum manual labour?
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Thank you,

Colin.