Saw this discussion when I tried to find the wing divider. I was the other bidder that day.
My Grandfather used this thing all the time. However his tools were lost in transit from one location to another. He did this with one wing, but only after he matched the wings and marked an equivalent points on both ends of the feathers. He would just match each point to the ends of the rack, then push the the teeth down and make an equivalent section of wing. He did this from both feathers and counted down the number of sections. He didn't often use the wing tier clip, he was faster at combining the feathers, then saddling along the hook and tying them down. Usually the sections were close in configuration. He didn't often use the wing tier clip, he was faster at combining the feathers, then saddling along the hook and tying them down. He was a master at match and attaching the wings.
The alternative to this device besides the bobbin approach, is accomplished using handle of an X-ACTO knife . You unscrew the collar l cated at the top of the handle to release the blade. You will have a slit in the aluminum handle. You cut an pieces of paper clip wire. the length of 3/4 inch. Sharpen both ends, smoothing the ends with fine sand paper (prevents hang ups in the feathers. Bend the wire into a horse shoe configuration such that both ends of the horseshoe configuration are equal. Then insert the wire into the slot where the X blade would be inserted into the handle. You tighten the collar. The doing the same feather matching and putting on the corresponding matching marks, one proceeds down the feather separating portions of the feather into equal matching amounts. Actually this method allows you to cleanly separate the entire matching sections of the the feather.
He was also very good at just looking at the two feathers, matching the sections, marking the section, cutting of the feather from the stem and separating these sections with a bobbin. But he made these flies all the time in those days.