Go look at Barshim's jump last year in New York. A monster leap that looked at least a good 8'4", AT LEAST. The bar was set at 7'10" however.
The long jump is a little more pure, if you hit a Beamon it will go down. There is wind and foul. (I like putting a giant windbreaker behind the runway, although it will block some audience, as for fouls mark their take off point within a jumping "zone")
But for High jump you are stuck where the bar is. Maybe something like how they measure vertical leap. I dunno, but it's frustrating to think that the high leap ever is not recorded. Any ideas?