Can't figure out how to get my offset function to work correctly in VBA

The code works great fills in all the values. Problem is I'm already offsetting to get my "number1" but I need to offset "DIA" at the same time to get it to stay with the "number1".

Basically I need to select two different cells and have them offset one cell down at a time together.

Sub calctest()
Dim number1 As Double
Dim number2 As Double
Dim answer As Double
Dim SFM As Integer
Dim RPM As Double
Dim MAX As Integer
Dim ALPHA As Integer
Dim DIA As Double

SFM = InputBox("What is the SFM?")
ALPHA = InputBox("What Alpha symbol are you using?")
MAX = InputBox("What is maximum RPM for machine?")
DIA = Range("b23").Value

Sheets("Feeds and Diameters").Select

If ALPHA = 1 Then
ALPHA = Range("d23").Select
ElseIf ALPHA = 2 Then
ALPHA = Range("e23").Select
ElseIf ALPHA = 3 Then
ALPHA = Range("f23").Select
ElseIf ALPHA = 4 Then
ALPHA = Range("g23").Select
ElseIf ALPHA = 5 Then
ALPHA = Range("h23").Select
ElseIf ALPHA = 6 Then
ALPHA = Range("i23").Select
ElseIf ALPHA = 7 Then
ALPHA = Range("j23").Select
ElseIf ALPHA = 8 Then
ALPHA = Range("k23").Select
End If

Do Until Selection.Offset(0, -2).Value = ""

RPM = SFM * 3.82 / DIA
If RPM > MAX Then
RPM = MAX
Else
RPM = RPM
End If
    
number1 = Selection.Value
number2 = Round(RPM, 0)

answer = number1 * number2

Selection.Offset(0, 13).Value = Round(answer, 1)

Selection.Offset(1, 0).Select
Loop

End Sub

I am soooo close to my desired outcome, feel free to ask any questions.
I can send over the file I'm working on if interested as well