Oscilloscope on an IPhone

Another example of a sensor connected to a smartphone.  Here a multiple signal Oscilloscope. A device which was an early introduction of mine to electronics.  Used to observe the wave shape of electronic signals, it was an early example of data visualization, well before computers were common. Forms of  the device existed as early as 1899, and cathode ray tubes were connected in the 1920s.  Another step forward.