Cesar and wsuraiderwi, you both hit on something I typed out in my post and removed. If I were to wear a GPS, I don't think I could resist the temptation to look, being the numbers guy I am. Personally, I do much better just hearing splits along the way when they are given. I use them more as a sanity check than anything and I rarely, if ever, respond to a split I hear by adjusting my effort level.
If you hit a mile split and are shocked by the result and you have to speed up or slow down dramatically (assuming the split is correct) then you have not trained yourself properly to race at the pace that you expected.
Let's see, I've already used “Precisely” and “Exactly” on this thread. I'm too tired to come up with another one so sorry that you're getting seconds for such a good thought but…Precisely.