if your series starts in A1, then B1 = 1 and B2 would be
=IF(A2=A1,B1+1,1)

"cynthiabryant" wrote:

I have seen this befroe but can not locate. I need to implement a counter
based on a previose cell. If it have

123
123
124
125
125
125
125
I need
123 1
123 2
124 1
125 1
125 2
125 3
125 4