Got me, no telling I guess, unless you talked to the engineer. It doesn't really matter after you understand their lingo. Looks like Provari would have gone with Co or cr for check ohms. Seems like they would have used Vu and Vd instead of P being as Power is measured in watts. Maybe the Provari can't make v's either.
Actually I just read some countries use u for voltage so you might be right. I forget these are made for the whole world.
I always assumed Ao was "atomizer ohms". Power up and power down seemed very intuitive.....