I don't think you can code the + and - keys, as they put any cell directly
into edit mode. So how about the left and right arrow keys
in the code below, the tow keys set a value to increase or decrease a cell
or cells by . this handles multiple cells
Option Explicit
Sub setkeys()
Application.OnKey "{right}", "IncreaseCellValue"
Application.OnKey "{left}", "DecreaseCellValue"
End Sub
Sub unsetkeys()
Application.OnKey "{right}"
Application.OnKey "{left}"
End Sub
Sub IncreaseCellValue()
ChangeCellValue 0.25
End Sub
Sub DecreaseCellValue()
ChangeCellValue -0.25
End Sub
Sub ChangeCellValue(amount As Double)
Dim target As Range
Dim cell As Range
Set target = Intersect(Selection, Range("range1"))
If Not target Is Nothing Then
For Each cell In target
If IsNumeric(cell.Value) Then
cell.Value = cell.Value + amount
End If
Next
End If
End Sub