How a fischer paykel determines your water level is actually very interesting and falls into the realm of quantum mechanics.

Washing machines DONT have a sensor that knows how much clothing you put into them. Rather what they do is spin the tub back and forth and gather data through the current being used to spin the tub back and forth.

This here is a simplistic example of the algorithm in use.

The very same algorithm can also be used for other loads where you are unsure of the conditions in more than one context.

eg. Quadcopter may read data from prop(s) current. A wind/gust rather than relying on gyroscopics to counteract out of balance.

yes: you CAN make a quadcopter fly straight WITHOUT the gyroscopic sensor!

Other uses: determining out of balance conditions on many devices. AND knowing just how BAD it is, WHERE it is and how much is req to counterbalance.