Besides the function and range switches (sometimes they are in a
single switch), the analog meter may have a polarity switch to facilitate
reversing the test leads. The needle usually has a screw for mechanical adjust
to set it to zero and also a zero adjust control to compensate for weakening
batteries when measuring resistance. An analog meter can read positive and
negative voltage by simply reversing the test leads or moving the polarity
switch. A digital meter usually has an automatic indicator for polarity on itsdisplay．