One thing to note is that the Radio Shack meter has well documented errors at lower frequencies, and most of the test tones don't account for that. So, you can print a chart of numerical adjustments that take into account the errors and let you add/subtract from your readings to get the true value. If you use the Stereophile Test CD tones, or most of those you download, this will be true. The Rives CD already adjusts the tones, so you can skip the manual math step and not adjust you readings before plotting them.
This is way easier in practice than it all sounds. Here's a couple of other tips:
Get a handful of colored pencils or pens and mark tape on your floor to denote speaker & seating positions. Plot the graph in matching color. Tweak your position of speaker or seating and repeat.
Don't freak if you get some strange results. This is why we treat rooms, and many conclude that their room is the component that most affects the results.
If high frequencies are wacky, try panels at first and then second points of reflection. To smooth out bass peaks and troughs try bass traps in the corners behind speakers. Measure again, and you'll see what benefits you get...Cheers,