I had just finished my digital thermometer and didn't want to take it apart yet so I added a button to switch between the thermometer
and the sonar. Since it measured distance and I was watching Doctor Who at the time I dubbed this the sonic ruler.
Even though I live in the United States I like metric for measuring small distances. So that is why it is in metric.
(I've had people ask, I don't know why. People are weird.)
Sonic Ruler
