Digital voltmeters are instruments that measure voltage or voltage drop in a circuit. They use solid-state components and display values digitally. Typically, digital voltmeters (digital volt meters) are used to locate excessive resistance that may indicate an open circuit or ground. They are also used to identify low voltage or voltage drops that may indicate a poor connection. Digital voltmeters are connected in parallel (and never in series) with the circuit being tested so that the meter can tap a small amount of current. The positive lead is connected to the circuits positive side and the negative lead is connected to the circuits ground. The digital voltmeters internal resistance is the impedance, which is usually expressed in ohms per volt. This amount is relatively high in order to prevent the device from drawing significant current and disturbing the operation of the circuit being tested. The sensitivity of the current meter and the value of the series resistance determine the range of voltages that digital voltmeters can measure.