Most levels are accurate when new, but it's whether they're still accurate after a few knocks that matters.
Also need to take into account what you're using it for. If it's to run a piece of conduit up a wall from bottom to top, then it doesn't matter too much if it's 10mm out overall, but if you're using it to set a door frame, and that ends up 10mm out of true, you're going to be looking for lozenge shaped doors to fit.
Also need to take into account what you're using it for. If it's to run a piece of conduit up a wall from bottom to top, then it doesn't matter too much if it's 10mm out overall, but if you're using it to set a door frame, and that ends up 10mm out of true, you're going to be looking for lozenge shaped doors to fit.