Runway Visual Range is the visibility directly down the runway recorded at the average height of the eyeline of a pilot on touchdown (more detail is not given, even though this is vague.) It is reported when the prevailing visibility is less than 1500m. It is recorded at three places: touchdown, mid point and the stop end, but usually only the touchdown is given.
As the RVRRVRRVR —Runway Visual Range —Runway Visual Range is directly down the runway and prevailing is in all directions, it is likely that the RVRRVRRVR —Runway Visual Range —Runway Visual Range will be better than prevailing visibility.
RVRRVR —Runway Visual Range is obtained either visually or by a device known as a transmissometer, which measures how much strength a laser loses between the emitter and detector as it passes through the air.