I have two sheets, In sheet 1 column A is full of numbers, I want to delete
all the lines in sheet 2 where column B does not match any number in Sheet 1
column A.

I am currently using the following code for another aapplication, if you
could modify this it would help me understand what I am doing a little better

Dim rng As Range
Dim i As Long

Set rng = ActiveSheet.Range(Cells(1, "DL"), Cells(Rows.Count, "DL").End(xlUp))

'Work backwards from bottom to top when deleting rows

With rng
For i = .Rows.Count To 1 Step -1
If Not Trim(.Cells(i)) = Trim(UserForm7.TextBox1) Then
.Cells(i).EntireRow.Delete
End If

Next i
End With

Thank you