How to use custom validation
 

Hi all,

I want to limit the input order using custom validation. My case is as
following:

From a1 to a10, i want user input one by one in order, so I use custom
validation and my formula is =a1<"" . after I clear the Ingore Blank, it
works well. But I also limit the order of delete, that means user has to
delete from A10 to a1 one by one in that order so I use formula like:
=if(a2<"", A1<"",A3=""),when a2 <"" means user input data, so check the
above cell a1 and only when a1<"" user can input, when a2="" mean user
delete data, and check below a3 and only when a3="" user can delete a2.
inserting works fine, but whne deleting even the formula is false, user can
still delete data? Could you help me fingure it out?

Clara
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thank you so much for your help