LastModified Time Stamp changes after filtering

[acrosenfeldsmbc]

Hello All,

I need to create a Time stamp for everytime I change a cell.

For ex puposes, I enter
A1 Subject Header , B1 Time Header
500 in A2, B2 has Time Stamp of 10AM
600 in A3, B3 has a Time stamp of 11AM

Its 12pm now, and I filter line A, now all the time stamps automatically change to 12pm....
If I don't filter, all the time stamps remain the same.

I need to filter, but I do not want the Time stamps to change.

<<<<<This what I have in my MODULE>>>
Public Function Lastmodified(c As Range)Lastmodified = Now()
End Function


<<<This is what I have in Excel as formula>>>
Cell B1: "lastmodified((A1))


Could someone help?

Thank you