I have a database (workbook) of customers who come into my store every month.
I divided my workbook into many worksheets. All of the worksheets contain
the same row and column headings and are clones of each other except for the
data.
We update the data twice a month and the worksheets are divded to represent
specific dates.

I need to macro that will flag me upon a duplicate entry, and/or insert a
marker in an adjacent column that indicates the customer is already shown on
another worksheet within that same workbook. The fields (columns) that need
to be checked prior to notification/marking are, Lname, Fname, Phone.

Is this doable?