RadioShack Sound Meter

I don't really know the answer to your question, but I do know the RS meter is fairly inaccurate at certain frequencies. If you want to be accurate, you'll need a chart that shows the deviate at each of the frequency bands. I'm pretty sure you can find the chart on-line here or at one of the other audio forums.

TIC

Maybe this will help :

http://www.audioasylum.com/audio/general/messages/49147.html

Rives Audio Test CD has a 2nd set of tones that have been calibrated for RS meter.

You should point it up.

Point it up or it won't accurately read the SPL reflections from the back and side walls. Every reflection in the room affects the freq. response at your listening position. I suppose those calibrations would be of some value if there was any consistancy in the manufacture and responses between any two RS meters. BUT- They'll get you in the ballpark. For any real accuracy at all, each would have to be curved individually. The Behringer ECM8000 is the cheapest reasonably accurate mic out there. Better starts with the LinearX M31. Of course: they require a meter or spectrum analyzer to plug into. A good excuse to go out and find a Behringer DEQ2496(just for the pink noise source and 1/6th oct analyzer functions). If you were checking the SPL output or response of a speaker system in an anechoic chamber you'd aim the mic directly at the system.

If you want to measure room a bit more seriously go to Hometheatershack.com and download "Room EQ Wizzard" (or REW) then load the sound meter correction calibration file for the Radio Shack meter and follow instructions to measure room.