ORIGINAL: Dopler
Also, after market strings can change a bow speed dramatically.
Ding ding ding...
Someone asked me a while back what some of my secrets for getting a bow to shoot over IBO or over a bowtechs BC are... a good aftermarket string can net you as much as an extra 12-15 fps. And thats how I have Gary's Ally shooting over BC with an arrow that is 34 grains heavier and at 65#s to boot.