The King's Gold

A king has 100 elves that make gold for him. The bars are to be exactly 100g. Elves were chosen for the job because they can just feel the bar and tell its weight. One day the king finds out through the grapevine that one of his elves is making all of his bars at 99g and magically hiding the leftovers. In this day in age there is not an instrument precise enough to tell the difference between 100g and 99g and no elf would rat on another, so he is in a bit of a pickle. He prays to his god for a solution. His god comes and gives him a digital scale. It can handle any load and is very precise. Being a spiteful god he only lets the king use it for one weighing. After that it will disappear. How can he find the thieving elf?

Part 2
If we change the problem from one elf to at least one elf how do we find out which are stealing?