Save office modification records in cell annotation VBA

Dim ydtext as string 'original cell value
Private sub worksheet_change (byval target as range)
If target. cells. Count = 1 then
Dim mycom as comment
Dim ybzstr as string 'original annotation Value
'------------------ Determine whether an annotation is added
Set mycom = target. Comment
If mycom is nothing then target. addcomment
'---------------- Edit the annotation content
Ybzstr = target. Comment. Text
Target. comment. text text: = ybzstr & CHR (10) & format (now (), "yyyy-mm-dd hh: mm") & "original content: "& ydtext &" changed to: "& target. formula
Target. Comment. Shape. textframe. autosize = true
End if
End sub

Private sub worksheet_selectionchange (byval target as range)
If target. cells. Count = 1 then
If target = "" then
Ydtext = "null"
Else
Ydtext = target. Text
End if
End if
End sub