Got this idea from a post on BoingBoing about a coffee freshness monitoring device
, and adapted it to a dog-fedness monitoring device. Quite handy if there is more than one person feeding the dog (or if even one of them is forgetful about such things, like me.)
Just take two disposable cups of any kind that nest. Put the arrow on the top one, and the arrowees on the bottom. Rotate to set.