The Meaning of Life, the Universe, and Everything.
Is it true that the anvil adds "a bonus of 12% of the maximum durability" when combining two items while the grindstone only adds "5% of the tool's maximum durability"? A crafting table does not give a bonus to durabilty as far as I can tell when combining items.
If I'm trying to combine several looted tridents to make a fully repaired one it seems the anvil is the better choice - and then run the repaired trident through a grindstone to remove prior work cost from the anvil.
Is that the best approach if I don't care about the XP cost on the anvil?
When combining items on the Anvil, "The target is repaired, adding the durability of the sacrifice plus a bonus of 12% of the maximum durability, up to the item's maximum durability. If the target item is undamaged, there is no charge for repair, otherwise the cost is 2 levels."
The bonus for repairing a Trident on the grindstone is also 12%.