The edit selected item is very broken. I did a lot of testing and it appears splitters break it out right as soon as an item passes into it until you delete them all and mergers break it if any items are currently moving on the belt through it. This was tested from a brand new game. There may be more things effecting the stored value as well but these are the ones I was able to confirm.
[Edited by SVLouie, 3/11/2020 10:12:30 PM]
I literally have no idea what you are talking about.
Pick up a slug, modify the amount after clicking on the item in the inventory, then you have that amount of the item.
No idea if it doesn't work or doesn't stick on some items.
If the option is useless let me know and I will remove it. In fact, it's the option that I have to spend the most time updating on this endlessly patching game that has no idea when it's going to be finished or what they are going to add or remove or change next.