How many did you communicate today?

Occasionally someone will knowingly remind us that "Studies have shown that only 17 percent [or some similar scientific-sounding value] of our communication is verbal - through words. All the rest is non-verbal, or meta-verbal." Hmm.. Does anyone know how they measure communication? What were the signals or events the researchers measured to figure this out? Words, syllables, eye-blinks, nods, winks, smiles, frowns, gestures, hand-clapping, foot-stomping, chuckles, belly-laughs, throat-clearings, yawns? Seventeen percent of what?