I think you'll find it's to do with the 'sensitivity' of the receiver. When you're tracking a localizer you want to know quickly if you're drifting off track whilst in NAV mode slight drifting is less imoportant so for a particilar deviation from the nominal track the needle will show a greater swing in VLOC mode than in NAV mode. It's a long time since I used thought about such things but I seem to recall that one box I've used was five times as sensitive in VLOC, i.e. a one degree deviation in VLOC would give one a dot deflection whereas in NAV you got the same one dot when you were five degrees off track (or something like that).
Edit - Sorry, I thought they were buttons but on re-reading the original post I see they are indicators.
Last edited by Spitoon; 4th October 2005 at 18:09.