I think I am out of my depth on this one due to my lack of experience with user forms….
If I try to step through the macro
Private Sub txtdelta_AfterUpdate()
then a UserForm springs up and nothing else happens.

I have never experienced anything ever like that before.
In my experience I can step through a macro to try to find out what and where any problem is.
If I try to do that with your macro , it does not let me step through it. Instead a UserForm pops up.

So I am at a loss on how to go further . Sorry
I don’t know how to find a problem in a macro that I can’t seem to run.
Hope someone else can help.

Alan