Mexico City and Sestriere have previously been the sites of records in the sprint and jump events. See effects of high altitude on humans. Records set at high altitude venues are often marked with an "A" though that does not disqualify it as a record. Under those circumstances, a "sea level" best is also tracked by statisticians. Long-distance races run at altitude, with less oxygen available to the athlete, have been shown to be to the athlete's disadvantage. In road events, the course is not required to be a circuit, but the overall decrease in elevation between the start and finish shall not exceed 1:1000, i.e. 1 m/km. In road events, the start and finish points of a course, measured along a theoretical straight line between them, shall not be further apart than 50% of the race distance. Bonus payments Witnessing a world record brings great pleasure for athletics fans, and athletes' personal sponsors and promoters of major meetings such as the Diamond League and its predecessor, the IAAF Golden League have offered bonuses to athletes breaking a record. Some middle-distance runners have specialized in acting as pacemakers in longer races, receiving a fee without even finishing the race, and possibly a bonus if a record results. This is a useful occupation for athletes who are capable of running accurately to a specified pace, but not capable of the fastest times to become champions in their own right. In the pole vault record bonuses create an incentive for an athlete capable of smashing a record to instead break it by the minimum amount (one centimetre), multiple times, at multiple meetings, in order to accumulate multiple bonuses. This has been done by Sergey Bubka in the men's pole vault, and Yelena Isinbayeva in the women's pole vault. Some commentators have complained that neither athlete ever posted as high a mark as they were capable of. In most other disciplines, this issue does not arise, since it is practically impossible to deliberately break a record by a small margin. World records World Athletics (then IAAF) commenced the recognition of world records in 1912, and indoor world records after 1987. In 2000, IAAF rule 260.18a (formerly 260.6a) was amended, so that "world records" (as opposed to "indoor world records") can be set in a facility "with or without roof." This rule was not applied retroactively, and has, thus far, only affected the men's