This is a Voltage Probe that lets you know voltage at any wire or pin in the circuit.

It works as a digital probe as well, changing to orange when a "high state" ( >2.5 V) is found.

To read voltage: hover probe over wires or pins to see voltages at any point of the circuit.
You can connect it with a wire to any part of the circuit as well.

To get available options Right-click on probe for context menu:

- Add to Plotter:
    Open Plotter in bottom panel and plots probe voltage.

- Remove from Plotter: 
    Remove probe from plotter.

See Plotter tutorial

Tick: Time lapse betwen 2 vertical marks.

You can add up to 4 probes to plotter, each one is maked with a color similar to plotter: