Above 2.0 m/s of tailwind a long jump still counts for the competition but no longer for record lists. Wind is measured 20 m from the board, 1.22 m up.
That small number next to the distance on the scoreboard isn't decoration. Above 2.0 metres per second of tailwind a long jump stays valid for the competition — you can win with it — but it never enters a record list. The most famous case: Carl Lewis jumped 8.91 m in 1991 with 3.0 m/s and it wasn't ratified as a world record; Bob Beamon's 1968 jump sat exactly on the limit. Measurement is standardised: the gauge stands 20 metres from the take-off board, 1.22 metres above the ground, and reads over 5 seconds, starting the moment you pass the mark 40 metres out. So a \"+2.1\" is a reading, not a judgement call. The usual thinking error is writing off a windy competition as worthless. Placings, medals and qualification all count as normal. The only thing that changes is how comparable your distance is.