I know this isn't the Field Calculator but one way to do it is using an update cursor.I just roughed out some python code, so it's untested but you could try this:import arcpy
FC = "C:\\YourFeatureClass"
SORT_FIELD = "F1"
F2 = 1
# Create update cursor to populate F2
rows = arcpy.UpdateCursor(FC,"","",SORT_FIELD, SORT_FIELD + " A") # Sort FC ASCENDING on F1 field
currentstate = ""
for row in rows: # Loop
if currentstate != row.SORT_FIELD:
currentstate = row.SORT_FIELD
row.F2 = F2
rows.updateRow(row) # Populate F2
F2 += 1
del row, rows # Delete to clear locks
Joel