General :: How To Define Variable In Form As String Which Can Work With Any Event

I have a form (Datasheet). I need to define some variable in form as string, which can work with any event. E.G in column "A"on event after update, in column "B" on event after update...

I will try to explain with a simple example : form (datasheet) columns: "A", "B"

on event after update in coulmn "A", I could have some like this:
(variable what I need to define) = 3

on event after update in coulmn "B", I could have some like this:
If (variable what I need to define) = 3 then
msgbox "ok"
end if

Now I try to work around the problem and use another column "c" to keep the value from after update A - but I know that, it's bad solution -Right?