My baselines are relatively simple to get to. You wont need measuring tape or anything crazy just the athlete’s body. Once you get into the basic position you can adjust the athletes measurements as needed.
Many times you’ll see athletes in a football combine or other event run the 40yd dash or another sprint. Before they start some of them are “crowding the line”, this is something I’m not a fan of at all. Crowding the line puts your shin angles in a position that points more “up” as opposed to “out”. I like to get a starting position with the best angles by having the athlete put their front leg or “strong leg’s” knee down a just tad (one inch) behind the line. Have the athlete stand up keeping the feet exactly where they are. The back leg or “smart leg’s” foot should be one foot length behind the front foot’s heel. Their feet aren’t on a tightrope so the back foot shouldn’t be directly behind the front, they can get comfortable so put some space between them to provide a good base.
Once you have these “measurements” you can have the athlete get down in a three or four point start. Be sure they keep their core tight and back straight. Hips should be just above the shoulders in the “set” position or just before the athlete begins to run.