On police ops at night in a high hover it would be nice to know my relative airspeed. It is sometimes necessary to hover downwind to keep the rear seat observer 'eyes on' with the 'person or vehicle of interest'. It would also be handy when doing tail rotor handling checks during airtests. How many of us have to 'guess' what sideways and backward speeds we are doing when checking tail rotor authority. Doppler and GPS can help, but both give ground speed and you have to compensate for wind. I would like to see this technology asap.