  We present a multi-tip scanning tunneling potentiometry technique that can be
implemented into existing multi-tip scanning tunneling microscopes without
hardware changes. The resulting setup allows flexible in situ contacting of
samples under UHV conditions and subsequent measurement of the sample
topography and local electric potential with resolution down to \AA\ and \mu V,
respectively. The performance of the potentiometry feedback is demonstrated by
thermovoltage measurements on the Ag/Si$(111)-(\sqrt3\times\sqrt3)\rm
R30^{\circ}$ surface by resolving a standing wave pattern. Subsequently, the
ability to map the local transport field as a result of a lateral current
through the sample surface is shown on Ag/Si$(111)-(\sqrt3\times\sqrt3)\rm
R30^{\circ}$ and Si$(111)-(7\times7)$ surfaces.
