Russell Dawson;2862181]Am I correct in thinking then that the workbook you have uploaded is the Master and will not change other than being added to I suppose when new alarms are introduced?
You are correct no new alarms will occur just repeats of the current list.

A daily process takes place whereby sheet2 is populated with new data (alarms that have been initiated (is that "set off"?)) and sheet1 (currently "Full list") is compared against it and any matches are highlighted on sheet1 depending on the priority level. Am I right?
You are correct just used sheet 2 as an example bare in mind there is currently no priority from the daily DCS alarms thus I want create a sheet which flag the Tag Name which are unique which have High priority

What does the new data for sheet2 look like or is it exactly the same as on sheet1 but presumably much shorter?
Sheet 2 will just be the amount of alarms that occur on that day