My team is developing an application on a mobile device involving a lot of scanning of barcodes (industrial applications, yay). Mobile = limited real estate.
In a particular case, we need the user to scan a subset of items. As an example: they have 12 bags in front of them, and we want them to put these items into bags 4, 5, 7, 9 and 12, scanning the bag as they do so. But we don't want to specify an order. We just want them to scan those 5 of 12, in any order.
We'll catch them if they do the same one twice, or the wrong one, give them a beep or something to say "nono, not that one". Technical-side, the problem is straight-forward.
What we're stuck on is how to display to the user "You have completed 7 and 9, but not 4, 5 or 12." Some visual way to describe that to them, so that if they are like me, and tend to zone out for a moment and forget what they were doing, a quick glance at the screen lets them know "You finished these ones, and still have to do these".
As far as we know, we should never expect the size of the set of bags to exceed 12 (but maybe next year we get told it now needs to be 24).