Also known as: きこりの泉
Kikori no izumi!
One of the gadgets from Doraemon. based on Honest Axe, one of Aesop'S Fables.
It allows the user to insert anything in the spring, and the water deity robot inside will offer a superior counterpart of an inserted item, then ask the user which item they dropped, and she will either give the superior item or not depending on the user's honesty.
However, the inserted item cannot be retrieved, and the spring can only be used up to 5 times.