Maybe you could use the doubleclick to add and the rightclick to subtract.
If you want to try it, rightclick on the worksheet tab that should have this
behavior. Select View code and paste this in:
Option Explicit
Private Sub Worksheet_BeforeDoubleClick(ByVal Target As Range, _
Cancel As Boolean)
Dim myRng As Range
Set myRng = Me.Range("a1:A15")
If Intersect(Target, myRng) Is Nothing Then
Exit Sub
End If
Cancel = True 'stop any edit in cell
On Error GoTo errHandler:
With Target
If IsNumeric(.Value) Then
Application.EnableEvents = False
.Value = .Value + 1
End If
End With
errHandler:
Application.EnableEvents = True
End Sub
Private Sub Worksheet_BeforeRightClick(ByVal Target As Range, _
Cancel As Boolean)
Dim myRng As Range
Set myRng = Me.Range("a1:A15")
If Intersect(Target, myRng) Is Nothing Then
Exit Sub
End If
Cancel = True 'stop rightclick menu from showing up
On Error GoTo errHandler:
With Target
If IsNumeric(.Value) Then
Application.EnableEvents = False
.Value = .Value - 1
End If
End With
errHandler:
Application.EnableEvents = True
End Sub
I added/subtracted 1, but you could use any number you want.