When a faucet??s friction is not enough, The faucet is rotated easily. so when the children and the blind use it, they can burn theirselves on the hot water. also, when the public use it, they can be hard to control the temperature exactly. To make up for the demerits, we applied to the existing faucet with spring and sawtooth. so, this is good at the controling temperature and we can prevent burning oneself on the hot water.