I pulled this off the web after google-ing "ballast Checker"
To verify which type of ballast is currently installed in a given fixture, without having to take it apart, a flicker checker is available through Motorola (call 1-800-453-1506 for information on obtaining this inexpensive tool, known as a flicker checker device [FCD]). Spin the flicker checker on a flat surface underneath the fluorescent lamp in question. If the ballast is the older, electro-magnetic type, you will see a stroboscopic effect appear as it spins. If the fixture has the high-frequency, electronic type ballast, you will see no effect on the flicker checker
Enjoy the toy
pennpoint