What is indicated by a voltmeter reading of 0.0V on a known working circuit?

A voltmeter reading of 0.0V on a known working circuit primarily indicates that there may be a faulty connection within that circuit. In an operational circuit, we would expect a certain voltage to be present. When the voltmeter reads zero, it suggests that there is an interruption in the flow of current, which could be due to various factors such as a loose wire, a broken component, or a poor connection somewhere in the circuit. This item indicates that the expected voltage is not being achieved, prompting a need to investigate the circuit for possible disconnections or defects.

In contrast, a fully charged battery would normally show a specific voltage rather than 0.0V, indicating that it's operational. Similarly, if the circuit were functioning normally, one would also expect a positive voltmeter reading. High impedance in a circuit can lead to low readings, but would not necessarily indicate a 0.0V reading unless accompanied by faults. Therefore, the situation points towards a connection issue, making it clear why identifying a faulty connection is crucial when faced with such a reading.