Need to fix the length of line to 80


I am using on my windows 7. I wish to fix the the length of line to 80 char.
setting-> editor->Max screen line length is fixed to 500. Try to change it to 80. but by default it shows 500 again.

Please help me to fix the line length


This is the same behavior I experience. All values below 500 get reset.


How to fix the length to 80 ?