HOWEVER...

Radar Knows What is Coming or Going
DSR is a revolutionary new police radar that features moving direction sensing technology. This breakthrough technology allows the DSR to know if targets are approaching or going away from the radar - in both stationary and moving modes.

ALSO
True Doppler Audio
The audio tone from conventional radars will vary in pitch when the patrol car's speed changes. The audio in the DSR is compensated for patrol speed, so the pitch always is directly related to the actual target speed. This allows the operator to know target speeds just by hearing the pitch, eliminating the need to constantly watch the display.

so,,,,
chances are,.. his unit auto-compensates for this using this "dsr" and gives an accurate reading.

so you may have some difficulty proving that he read the reading wrong or it malfunctioned

you might want to find out what model # he used.

and a lawyer with traffic experience can help with these things.