LS 15 0.2mm line of sight error

Hello I have adjusted line of sight first time it was last summer, error was 1.2" , second time it was 8 month ago it was 4.3" after that 5.3" and today 7.7" and I wander is that normal?
second question every time before I have done line of sight adjustment I do level bubble adjust and after line of sight is that true?
thank you for help in advance

 

If the level accepts values, it is normal.

You can only do it once, no matter when

 

I do very precise work and every time before start doing this