Zumo 550 fuel tank count down

[Kingsized]

I posted this in the wrong area first so this is a re-post.

I have searched but can't find this answer. I have read comments and heard from people that state that you can make your fuel odometer count down instead of miles driven. A friend has a 660 and his does this by counting miles left, which is easier when your figuring mileage to your next fuel stop. I can't seem to find it in the settings and in the manual, it doesn't state how. All I see is how to reset the fuel gauge and of course to set the miles per tank.

Anyone know how to do this assuming it can be done?