It also matters a lot as to how accurate your person taking spilts is. Some parents will come unglued when I tell them their kids' splits because their split was a lot faster than the one I recorded.
Every year I try to explain how to take accurate splits for the 4x400, and I often end up with blank stares.
How to take splits for your kids' 4x400 meter relay team(for you parents out there):
1) Gun goes off = Start watch on smoke, not sound of gun
2) 1st exchange to 2nd runner (lead-off runner's split)
a) 3 turn stagger: take split when baton crosses the 800m start line for that lane
b) 2 turn stagger: take split when baton crosses the finish line
3) 2nd exchange to 3rd runner (2nd runner's split): take split when baton crosses the finish line
4) 3rd exchange to anchor runner (3rd runner's split): take split when baton crosses the finish line
5) Anchor runner's split: when runner crosses the finish line
I love it when I get the parent of the lead-off runner (on the 3 turn stagger) telling their kid that they'd PR'd by almost 2 seconds when they've stopped their watch when their kid crosses the finish line.