The purpose of a fuse or circuit breaker is

Fuse or circuit breaker is used for the safety purpose in electrical circuits.

This fuse has property that it has low melting point due to which as large amount of current will flow through the switch then it will melt down due to thermal effect of current given as

so due to large flow of current heat will be more in fuse wire and it will melt down due to more thermal energy.

So fuse is used to protect the electrical appliances such that when large current will go through the fuse then it immediately break and stop the flow of current so if fuse is not used in them then large current may damage the electrical appliance.

that tool is called an altimeter which measures your altitude which can be used to tell which atmosphere you are currently in, including the stratosphere.

hope this ! : )