Decrease item damage exactly 1 point

I am trying to damage an item in a slot by exactly 1, but you can only do percentages. This makes some items with a max_damage under 100 not change at all because of rounding issues. I'd like to decrease it by exactly 1 every time, but this doesn't seem possible, except maybe with some scoreboard calculations or something? item modify entity @s armor.head {"function": "minecraft:set_damage","damage": -0.01,"add":true}