In the words of Dunlop:

Create incredibly smooth volume swells or control your effect pedal
parameters with the Dunlop DVP3 Volume X. Small and pedalboard-friendly,
the DVP3 is solidly-built and ready for the road. Its housed in an
aluminum chassis with aggressive non-slip tread and comes equipped with
our patent-pending Low Friction Band-Drive for a smooth range of motion
without the fear of breakage or change in feel or range. For maximum
comfort and precision, the DVP3s rocker tension is fully adjustable.

When using the DVP3 as an expression pedal, you can use the internal pot to set the minimum level of the parameter youre controlling with the
rocker. If you want to reverse the function of the heel-down and
toe-down positions, the DVP3 has an internal switch that allows you to
do so.

Along with Volume, FX and Output jacks, the DVP3 also features a convenient Tuner output for silent tuning onstage.