This device by Dejan Nedelkovski of How To Mechatronics implements both an ultrasonic sensor for range measurement and an accelerometer for measuring angles. While you’ve likely seen these implemented separately in other projects, combining them saves space, and allows the Arduino Nano onboard to use the two readings together to calculate a square area automatically.

User interface consists of a power switch, along with a single button for program interaction and to choose between the different measurement routines. Results are displayed on an LCD screen, and the electronics are encased in clear acrylic for visibility. 

Code and PCB files are available on the project’s write-up, and the video below gives a nice overview of its functionality and build process.