World records in athletics are ratified by World Athletics. Athletics records comprise the best performances in the sports of track and field, road running and racewalking. Records are kept for all events contested at the Olympic Games and some others. Unofficial records for some other events are kept by track and field statisticians. The only non-metric track distance for which official records are kept is the mile run. Criteria The criteria which must be satisfied for ratification of a world record are defined by World Athletics in Part III of the Competition Rules. These criteria also apply to national or other restricted records and also to performances submitted as qualifying marks for eligibility to compete in major events such as the Olympic Games. The criteria include: The dimensions of the track and equipment used must conform to standards. In road events, the course must be accurately measured, by a certified measurer. Except in road events (road running and race walking), the performance must be set in a single-sex race, with the sole exception of the mixed-sex 4 × 400 m relay, introduced by World Athletics in 2017. All team members in a relay race must be of the same nationality. Pacemakers are allowed, provided they have not been lapped; lapped athletes must give way. Drug testing immediately after the performance is now required for ratification of a record. Existing records which predate this requirement are still extant. Athletes who pass the immediate test but are later found to have been using banned substances have their performances invalidated. In running events up to 200 m in distance and in horizontal jump events, wind assistance is permitted only up to 2.0 m/s. In decathlon or heptathlon, average wind assistance of less than 2.0 m/s is required across all applicable disciplines; and maximum of 4.0 m/s in any one event. As an exception, according to rule 36.2, specific event organizers may choose to ignore wind velocity readings exclusively for their specific event records (e.g. a performance in a 100 m race at a meeting with a wind reading of +2.4 m/s may be considered that specific meeting record, but will not be considered as a world record). In running events up to 800 m in distance, photo finish fully automatic timing is required. There is no restriction on altitude; since the thinner atmosphere of higher altitude provides less air resistance, locations such as