Maybe these will help, Randy.
Essential Accessories: The Radio Shack Sound Pressure Level Meter
A Quick Overview of Home Theater Calibration
The Radio Shack SPL meter isn't completely accurate. Should you wish to chart your system's frequency response using tones at specific frequencies, here are the corrections for the meter. Whatever your meter reads, add or subtract the amounts in the chart. When using a 100Hz tone, if your meter reads 75 dB, you're actually hearing 77 dB (75 on the meter +2 dB from the chart = 77)
These corrections do NOT apply when using the pink noise from your receiver or from the Avia or DVE discs when calibrating your system
Radio Shack SPL meter corrections 
