A couple of thoughts... If you need calibration you need to use a piston calibrator like the one in the link Mac provided. You'll need to make sure the calibrator coupling is the correct fit for your mic. Turn on the calibrator, tell Smaart the level the calibrator is built to provide. You're done, unless you need to import a correction file for your mic.
An alternative is to use the line output of your Rat Shack meter to drive Smaart. Run up pink noise until you're at some arbitrary level, say 100dBC (or flat if you have that option). Tell Smaart whatever level the meter says. No, you can't use your measurement mic without your levels changing...
If you're monitoring SPL while using the spectrograph at FOH (and aren't concerned about things >6kHz) this may suffice; I certainly wouldn't consider it for system tuning.
Rational Acoustics just announced new Smaart training dates with Jamie Anderson and Harry Brill teaching. If you've not taken a class, Al, I suggest you do so. I retake it every few years because I can be a big dummy and get set in my ways. At any rate, Rational has classes in January and February which are traditionally slow work times for a lot of folks... something I've asked for every time I've talked to Barb or emailed Karen. Y'all get yourselves some skoolin'. No foolin'.
Have fun, good luck.