Charles,

I would suggest that you could add code to the On Enter of the Quantity
field that would ask the user for the change in the quantity. But, if
you do that, I would lock the quantity so it could not be changed in
any other way.

So, to lock the quantity field, bring up the properties and on the Data
tab, click Locked and check Yes.

Then give the Quantity field a name - like lngQuantity - the name is
found on the Other tab of the Properties.

On the Events tab, find On Enter and click in the white field. Click on
the three dots and select Code Editor.

Add between the Private Sub and End Sub on blank lines:

On Error Resume Next

Dim lngQty As Long
dim strAnswer as String

'As a note, the following should all be one line
strAnswer = InputBox("What do you want to increment the quantity by? If
you want to lower the quantity, put a minus in front of the number.)"

lngQty = val(strAnswer)

if lngQty <> 0 then

    'The next line is also one line
    me.cboQuantity.value = me.cboQuantity.value + lngQty

End If

_____________________END OF CODE

This tells the computer if there is a problem just keep going.

Sets up two variables to hold the answer given and convert it to a
number.

Then, if the number is anything other than zero it is added to the
existing number.

Be sure to notice where I have left you notes for lines that should not
wrap.