For example,

A1 = 5
A2 = 6
A3 = 7
A4 = 5
A5 = 6

How can you highlight/change the cell colour of all duplicate
occurences of A1 in the row, in this case A4?

And when changed is it possible to keep the highlighted colour, in A4,
even if A1 is then changed to 6? and when it changes to again
highlight/change the colour of all cells in the column that match its
new number - in this case A2 and A5?

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i'm completely new to spreadsheets and feel a bit in over my head.

thanks,

Alice