Info on Voltage Limiter Operation

Frankly, I never paid much attention to the "dope" on the old units. "Back then" they usually work or they didn't. After all, you can't adjust them, LOL

But about the figuring. We don't have a sine wave here, I'm not sure RMS applies, but "my math" has been awhile. Why would it not be a simple percentage off 12-14V, that is 5V/ 14 or 40 something percent?