SecureCab- why lowest forward gear?

i have some questions about the pre-trip. I'm sure they're all very basic questions but, can't learn if ya don't ask.

why do you put your tractor into the lowest forward gear before taking the key out of the ignition during a secure cab procedure? why not neutral? or a higher gear, or reverse/park? what benefit does 1st gear have? is there a specific reason for this?

 

hmmm thanks for bringing this to my attention @Longarm I'll check it out. I'm not sure if the pretrip study materials i have tell me to use lowest forward gear for the air leakage test.

@ExOTR ahhh thanks. i bet that's what it's about. to keep it from rolling in the event that something goes wrong... I'm guessing

 

secure cab is when you enter the cab using 3 points of contact, place gear shift lever in lowest forward gear, pop air-brake control valves, remove key from ignition, exit cab using 3 points of contact and chock tire. Secure Cab is also done whenever exiting the cab of your tractor, throughout the rest of the pre-trip.

that's what I've been taught.