Durability Altering

Some of you might remember a post I made a few days ago looking to alter item durability, but I've hit another roadblock and I'm trying to understand it.. xD
/minecraft:item modify entity 0bviouslee weapon.mainhand { "function": "minecraft:set_damage", "damage": -0.0000000000000000000000000000000000001, "add": true}
Doing this adds one durability rather than removes, and the same goes for
/minecraft:item modify entity 0bviouslee weapon.mainhand { "function": "minecraft:set_damage", "damage": 0.0000000000000000000000000000000000001, "add": true}
(same thing without the minus)
Any idea on how I can just remove 1 durability from an item?