Lock a field
 

Hi all,
I'd like to know how to lock a field after pressing the next/previous
button on the record status bar. Some of the fields are only unlocked when
pressing the add button on my form. However, I found that the fields are
still unlocked with pressing the next/previous button on the record status
bar after pressing the add button on my form. Do you mind to advise which
event I should put the lock property to? Thank you for your kindness.