The tendency of visual range (e.g., upward, downward).  Defined for the purposes of aviation meteorology reporting of the visual range on runways (WMO No. 49-2).<br/><br/>If the [runway] visual range (RVR) values during the 10-minute period preceding the nominal observation time show a distinct upward or downward tendency such that the mean during the first five minutes varies by 100 metres or more from the mean in the second five minutes of the period, an UPWARD [U] or DOWNWARD [D] tendency is recorded. When no distinct change in RVR is observed, NO CHANGE [N] is recorded.<br/><br/>See WMO No. 306 Vol I.2 FM 94 BUFR code-table 0 20 018 "Tendency of runway visual range".<br/>