Problem With Union Method: Combining Two Ranges

I have the following two ranges in the same spreadsheet: A1:A1000 and B1:B1000. Both contain data that I would like to manipulate. Let's assume I would like to add "1" to every cell in the two ranges. This is what I have so far:




Sub Test2()
Dim wb As Workbook
Dim ws1, ws2 As Worksheet
Dim rng1a, rng1b, rng_union As Range
Set wb = ThisWorkbook
Set ws1 = wb.Worksheets("testsheet")
Set ws2 = wb.Worksheets("result")
ws1.Select
Set rng1 = Range(Cells(1, 1), Cells(1000, 1))
Set rng2 = Range(Cells(1, 2), Cells(1000, 2))

Set rng_union = Union(rng1, rng2)...................

Function ADDONE(rng)
n = rng.Cells.Count
ReDim rng_add(1 To n)
For i = 1 To n
If rng(i) = "" Then GoTo NextIndex
rng_add(i) = rng(i) + 1.............
End Function
I have to somehow combine the two ranges because the data needs to be manipulated simultaneously. Instead of having the range of results returned to me (see worksheetfunction.transpose), I could have calculated the variance, average etc... of the results, too. I'm using the transpose function to show that the operations in function ADDONE are only conducted for the first range of cells (rng1) that I have joined with the union method. I presume that Union might not be the correct method but I don't know ehich other method to use.