Use combo box to reorder fields

[Melinda]

I have a form that we are using to review medical records. There are 2
columns on the form, Column 1 is the ORIGINAL coding of the patient's chart,
which MUST be in a very specific order.

The second column will be used to either validate that the code in each
position is correct (check box that assigns the value from original field in
column 1 to same position in column 2), or allows the user to re-order the
original sequence.

I am using the following table and code in a combo box on the form to allow
the user to assign a new "position" (Sequence), to the value in each of the
original fields (original coding and sequence cannot change). The new
sequence is saved into another table that stores the updated sequence with a
one-to-one relationship with the table that contains the original sequence.

I can get the values into the right place with the code below. My problem
is that if the user wants to change the new sequence after it has already
been made, how do I (1) acomplish this, (2) prohibit the same sequence number
from being entered in more than 1 of the new fields?

tblPDXFieldNames
Sequence FieldName
1 CDX1
2 CDX2
3 CDX3
4 CDX4
5 CDX5
6 CDX6
7 CDX7
8 CDX8
9 CDX9
10 CDX10
11 CDX11
12 CDX12
13 CDX13
14 CDX14
15 CDX15
0 Null

Private Sub cboSequence1_AfterUpdate()
If Me.cboSequence1.Value = 1 Then
Me.CDX1.Value = Me.DX1
Else
If Me.cboSequence1.Value = 0 Then
Me.CDX1.Value = Null
End If
If Me.cboSequence1.Value = 2 Then (combo box for resequencing)
Me.CDX2.Value = Me.DX1 (CDX# = New Sequence Field; DX# = Original Sequence
Field)
Else
If Me.cboSequence1.Value = 0 Then
Me.CDX2.Value = Null
End If

Any help or suggestions for a better way to do this would be appreciated.

Melinda

etc......