Any info on a Laack Regulyt lens

Looking through my junk box, I found a Laack Regulyt lens. It' s 10cm in a Prontor II shutter. It has a knurled front element which turns on a scale of 0-3-6-10, so I assume it is a variable soft focus lens similar to a Wollensak Verito or Velostigmat II. The only thing my search turns up is that it is a three element lens. I have no idea what camera it was on.

Anybody know anything about it? I'm hoping it will cover 4x5, but maybe not.

My source from the 50s says it is a plain triplet, 105mm, covering 6x9cm

Thanks. Then perhaps it was on a folder and the scale is for focusing. I'll have to put it on a camera with ground glass and see what moving that scale does.