How to use a code to display the current date based on certain criteria

Requirement:

The user has a blank A-column that is starting from A600;
next to it a blank B-column that is also starting from B600

What the user needs is a code/formula/macro that whenever something will be inserted in column B (starting from B600) -> the column A will react by displaying the current date.

Furthermore what I really need is that the date will not change once it has been inserted.

https://www.ozgrid.com/forum/forum/help-forums/excel-vba-macros/1202772-freezing-the-time

Solution:

Copy and paste this macro into the worksheet code module. Do the following: right click the tab for your sheet and click 'View Code'. Paste the macro into the empty code window that opens up. Close the code window to return to your sheet. Enter a value in column B in any row >=600 and exit the cell.

Code:

Private Sub Worksheet_Change(ByVal Target As Range)
    Application.ScreenUpdating = False
    If Target.Row > 599 And Target.Column = 2 Then
        Target.Offset(0, -1) = Date
    End If
    Application.ScreenUpdating = True
End Sub

https://www.ozgrid.com/forum/forum/help-forums/excel-vba-macros/1202772-freezing-the-time

Obtained from the OzGrid Help Forum.

Solution provided by Mumps.