Getting an accurate reading on the high frequencies (above 10K) has been a real problem with inexpensive measuring devices like the Radio Shack meter. I've done a bit of experimentation using RS's analog meter and it's really not any use for the high frequencies. I guess the mics just aren't up to the task. It did great from about 40hz to 10K and was a lot of fun to mess around with.
I used JA's test disc.
It's a great way to get your wife to leave the house for a bit. On the downside, she'll probably go shopping and spend money.