Hmmm, dont agree about "People jump higher because they're getting better"
For those not good nor experienced, yes, but... those "max" jumpers who has jumped for years, are maybe and maybe not motivated even more now when you can measure the height and "compete" (agree with Hulb here), but NOT because they are getting noticeable better IMO, but there is a goal that can be measured now so they are aiming for this target of course, and we will see higher jumps.
Also, there will be some errors in the measurements, some might be freak errors of significant size (and noone really wants to dig deeper into the accuracy and errors, which I dont understand working with measurements full time at work ?) and give wrong results, would agree somewhat with ShaveTheWhales - but we know this is the case, and might still be able to count on the average jumps if comparing (but noone does that ha haa).
Anyways - a lot of fun and motivation now, not present as directly earlier