From your description, it sounds like a Public or Global variable  will work
fine. Is your macro something like this?

Public Prev As Integer

Sub TEST()
Dim x As Integer
'Set default value for Prev%.
If Prev% = 0 Then
Prev% = Selection.Rows.Count
End If
'Count the vertical cells selected.
x% = Selection.Rows.Count
'If 1 cell is selected, move Prev% * 3 columns
'to the right.
If x% = 1 Then
ActiveCell.Offset(x% - 1, Prev% * 3).Activate
Else
'If more than one cell is selected, move x% * 3
'columns to the right.
ActiveCell.Offset(x% - 1, x% * 3).Activate
End If
'Store the number of vertical cells selected this time.
Prev% = x%
End Sub