Variac Transformer.

I just received my Variac Transformer, Heavy little thing, great to control my fan.

Can someone explain a little more about the dial? random numbers from 0 to 130, Theres a little meter on the front from 0 to 150, 110 is a redline, what is that? if I pass the red line is that a bad thing?

Fan rated for 340 CFM, filter and one turn in my duct. How can I calculate my cfm from the numbers on the dial?

Thanks!

is it a tent grow? I use two one for intake and one for exhaust.
I try to keep the tent "full". they do not have to run on full I keep mine at 65%

It's in a cabinet build. I just want to makes sure I change out the air just enough with out it being near full power to cut down on some of the noise.

The numbers are not random; they are an approximation of the voltage you will get if you turn dial to that number which you can read on your 'little meter'. and yes bad things can happen if you exceed the rated voltage of your fan motor.

The '110' is standard US voltage out , so if you exceed that by going to 130(v) your fan will protest sooner or later and smoke; although running at higher speed . Going too low is another potential problem, drawing current but not turning sufficiently to carry away the heat generated by itself.

The Variac is an AUTO-Transformer in electrical jargon. The one I have is a Powerstat .
A word of CAUTION: Do NOT plug anything electronic into it as it could feed back a large surge as the magnetic field collapses after (when) it is turned off or unplugged.