it's very easy to overthink, or assume patterns/sequences, rather than the subtraction needed. especially with only the"bottom" row as example. it took me ages of staring at the grid:

7 ? 3
? 5 1
9 ? 7
? 9 0
5 0 5

to figure it out, and i wasn't at all sure i was guessing right. a second full row would have made confirming possible. i think it's a case of knowing the answer made the room designer think it's more obvious than it actually is. looking at it filled in:

7 - 4 = 3
6 - 5 = 1
9 - 2 = 7
9 - 9 = 0
5 - 0 = 5

helps a great deal. maybe asubtraction symbol/left to right indicator on the diagram or input pad would've gotten the idea across in a nice puzzle-esque way? Lots of work was put into the room, and it was great fun. this puzzle was just frustrating for many players sadly, including me.

thank you for your comments! I'm very grateful to your review, which helps me build my next rooms better to keep in mind of the difficulty level, hints, and smoothness for better gameplay :D