[Claus Busch]

Hi,

Am Tue, 29 Nov 2016 18:48:19 +0000 (UTC) schrieb tb:

The columns for current data go from B to J. Columns for new data go
from K to T. Column A holds the part number codes.

The problem is with the number of rows... As we keep on adding new
part numbers, the number of rows keeps on getting bigger. Right now
there are over 15,000 rows.

with 15000 rows or more a macro is also slow.
You better go another way and only mark the correct data. That is easy
with the advanced filter. But you need headers in both tables.
Then try:

Sub CompareData()
Dim LRowC As Long, LRowD As Long

With ActiveSheet
LRowC = .Cells(.Rows.Count, "A").End(xlUp).Row
LRowD = .Cells(.Rows.Count, "K").End(xlUp).Row

.Range("K1:T" & LRowD).AdvancedFilter Action:=xlFilterInPlace, CriteriaRange:= _
.Range("A1:J" & LRowC), Unique:=False

.Range("U1:U" & LRowD).SpecialCells(xlCellTypeVisible) = "OK"
.ShowAllData
End With
End Sub


Regards
Claus B.
--
Windows10
Office 2016