Proteus voltmeter value in simulation not right
I think that's what we call "floating": as long as that wire is connected to nothing, you can't know what happens.

It's quite realistic: if you turn on a multimeter and don't connect the Plus-Pin anywhere, it will show values.



To get around this, you can ensure that this wire is never connected to nothing by adding a resistor in parallel to the meter:







simulate this circuit &ndash; Schematic created using CircuitLab