Ah, thanks for that pointer, a bit more googling suggests that is what sets sweep and latch range. It's too late tonight, will have to play with it later in the week.
Among other things I've done in my life, I've done the generic "maintenance man" gig round about '85/'86 or so. Always made it a priority to pick up as much info as I could back in those immediate post-Uni days just to be able to BS my way through some skills. Seems still to be working.
Completely OT, but the best bits of education I ever got at Uni were the 6 months as a short-order cook in the townie greasy spoon. Seem to be the only bits I use today.
I saw garage door and immediately assumed the big one. For the record, there are garage door openers (car entry) that have locking devices that swing down of top of the door once it's fully closed. Good friend of mine is a Druid (tree surgeon, ala MASH) and has so much expensive stuff in his garage (at least a dozen high-end Stihl chain saws) that he opted for the extra security.
And then of course I've got this terrible pain in all the diodes down my left hand side.