Mastech and Volteq regulated variable DC power supplies typically come with displays for both voltage and current, which always shows the actual output, not the setting you input. To set the voltage limit, simply turn the power supply on without any load connected. The power supply is in "CV" mode by default, simply vary the voltage adjusting knob until the voltmeter shows the voltage limit you desire, this is the maximum voltage the power supply will put out until you adjust it again.