Meet Results - USATF Hershey National Junior Olympic Track & Field Championships - July 23-29, 2018
The "Improvement" column, on the report as "Improv", compares the athlete's performance to their best time, height or distance in the database.
A negative value is an improvement over their previous best.
A positive value is how far off the athlete was from their previous best.
A "---" means no personal best exists in the database for that athlete for that event.
Athletic.net results link.