Plate calculator.

Every plate, plus the bar. A count is how many of that plate go on altogether, so four 20 kg plates on a 20 kg bar make 100 kg. The bar is counted once, whatever is hanging off it.

Half of each count goes on each side, heaviest first, which is the order plates go on. The arrows move in pairs, so a count you build with them divides. Type an odd number and it stays odd: the spare plate is drawn on one side and the answer says the two sides differ, because they do, and rounding the plate away would report a weight that is not on the bar.

The bar comes off the total and what is left is halved, which gives the weight one side has to make. The fewest plates that make it are found by working up from nothing, which always finds the shortest stack there is. Grabbing the biggest plate each time happens to give the same answer on these seven plates; on a set with a 3 kg plate in it, it would not. Where two stacks tie, the heavier plates win: 40 kg a side is 25 and 15. A warm-up ladder then changes one plate a step, where the evener answer would have you strip the bar at every one.

Every plate here is a multiple of 1.25 kg, so a side can make any multiple of 1.25 kg and nothing else. A total that leaves an odd 1.25 kg once the bar is off cannot be split evenly, and the block says so.