Why is it called a "tri-burner"

Got a question for the 'experts' here. The common term here for a stove where the combustion fan is driven either by the stoker motor itself or only runs with the stoker is a "tri-burner" stove.

I don't have a problem with the term, but I DO want to know where the term originated. What's "tri" about it? Should it be "try-burner" - as in Try to make it Burn??

I'm sure somebody here has to know. Matthaus? Greg?

Maybe it would be a part of a residential stoker stove history lesson?

Thanks!

Chris

From: http://www.readingstove.com/company.html

Reading Stove Company uses the patented "Tri-Burner" Stoker System with a variable heat control.

As Yanche said the Reading Stove Co, is the only company using that design any more. The older style Alaska stoves all used it, and not sure if anyone else did.

I searched online for the patent and didn't find anything. I do have the one on your stoker unit that Greg sent me a while back:
http://www.freepatentsonline.com/4662290.pdf

Guess I will have to dig a little more, will let you know if I find anything.