This sounds anal, but if you want good results you have to start with accurate measurements. Here's how I did mine for my DD. I took video of her from about halfway up the first base line (third base would work also), being sure to include the catcher and making sure you can see the pitching rubber and home plate. You need these for reference and measurement. So you're perpendicular to the path of the pitch. Video several pitches - maybe a dozen or so - so you get a good sample of where her release point is.
Now comes the "guestimating" part. Watch the video on TV and freeze it right as she releases the ball. Now you have to estimate how far in front of the pitching rubber this release point is. Subtract this distance from 40'. Now look at how far the catcher's mitt is behind the back tip of home plate, and add this to the distance. This will give you the ball's actual travel distance for 95% of your daughter's pitches - close enough.
I'm not a math wizard, so I looked up the time/speed/distance calculations with Google. If you know how to use Excel, it's pretty easy to build a table to print out.
The hardest part for most people is starting and stopping the watch accurately. You have to start the watch just as the ball is at the release point, and stop it just at contact with the catcher's mitt (the measurement from the video experiment). Like anything, this comes with lots of practice. While your DD is practicing her spins, you can practice your start & stop timing skills. Pick a 1/100 second value (.45 for instance) and practice trying to stop the watch at that number. After a while, you can actually get fairly good at it (or else you'll get so frustrated that you'll chuck the stopwatch in the trash can!). Realistically, you should have a good idea of how fast your DD pitches anyway. If your readings are WAY off of that, you have introduced an errror somewhere.
Hope that helps!
