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I don't think I've ever explained the math to anyone outside the forum.  I would gloss over too...      I am curious how you explain the KS jig though... since "the science" is basically the same.  I do get that a "lay person" will appreciate a visual of seeing an actual angle vs. an arbitrary distance.

That's just it, I didn't "explain" the KS-123 rather just demonstrated it. Because the person had heard me talk about and show the other method, their take-away was it is much easier now.  Having to use an app to sharpen, even with the ease at which it could be done, just made it seem harder than it really was for some I think.

Depending on the knife blade/handle length, and perhaps whether you have the longer US-430 USB, you could even put the KS-123 onto the USB out past the stone, or even hanging down from the USB, and set the projection. Then the weight of the knife/jig helps ensure it is against the USB and the spring brings the v up to the knife edge. Then slide it over to set the angle on the stone. It is really quite flexible how you do it.

When I would show my friends the Tormek, I'd often spend some time talking about the math behind the calculator/app method, and demonstrate setting  up to sharpen a knife, measuring/adjusting things and all involved, and then the results.  Not everyone appreciates the science behind the results though.  For those who enjoyed it, it was a good story.  Most just glossed over it.

The other day I demonstrated the KS-123, with the same final results.  I got a much better response from the ease of setup without having to use an app, as the person seeing it was already familiar with the prior methods. The comments were it took all the tedious setup out of the process.

While I was happy using an app, the KS-123 makes it even more simple, and I think much more approachable, especially for those who don't appreciate the science.

(In fact, I'm not sure the spring is needed all that much.)

It may not be entirely needed, but I like that it is there.  It pulls the angled section into the blade.

I don't disagree.

What I did prior to answering earlier was tighten the "Knob for locking Protrusion" enough so that the spring didn't have any affect, and found that I could manipulate the jig quite well without the spring's influence.  But it is a convenient feature.

Oh yes, totally agree with this.  Once locked in place the spring has zero impact.

Not quite what I meant... I just tightened it enough to negate the spring, I could still slide protrusion piece back and forth to set the distance, without the spring doing anything... then tightened it down.

Sure, the key point being you negated the spring, whether locked tight or providing just the right amount of friction.

Regarding accuracy of the KS-123, my first post in this thread addressed my simple test and observed results. The Calcapp calculated USB height was just .1mm different than was set with the KS-123 and measured with an inexpensive digital caliper.  I think that is within measurement error and accuracy of my caliper.

(In fact, I'm not sure the spring is needed all that much.)

It may not be entirely needed, but I like that it is there.  It pulls the angled section into the blade.

I don't disagree.

What I did prior to answering earlier was tighten the "Knob for locking Protrusion" enough so that the spring didn't have any affect, and found that I could manipulate the jig quite well without the spring's influence.  But it is a convenient feature.

Oh yes, totally agree with this.  Once locked in place the spring has zero impact.

(In fact, I'm not sure the spring is needed all that much.)

It may not be entirely needed, but I like that it is there.  It pulls the angled section into the blade.

If I were to become a "knife only side job sharpener", I'd rather go with a variable-speed belt sander, a coarse-to-ultrafine-grit set of belts and a leather belt, a BGM 100, USB-430 and a knife jig.

Using this setup, curious how would you set up and ensure repeatable 15 dps (or 12, or 17)?

Great to hear. I have 2 support bars so for knives I will be setting one for honing and one for sharpening. I will use my jig for setting the projection distance on each knife. Going this the new KS-123 won't be used too much unless someone wants a different angle.

I also have two USB, the one on the honing side in a MB-102.  When switching knives, I set the projection, then I've just been setting up both sides with the KS-123 since it is so quick, then on to sharpening.  So far with the knives I've been doing I've not been able to maintain the same projection between knives with the KJ-45.

My KS-123 arrived today. I first set up to sharpen a kitchen knife using the KJ-45 jig with the KS-123. After getting it all adjusted, I then measured the projection and entered the values into Calcapp which said the USB height should be 88.6mm. Measuring this after the angle setter was used yielded 88.7mm.  I'd say this is well within specs of my inexpensive digital caliper used to take the measurement.

Even the first setup was quick after having watched the Tormek video.

I then used the angle setter to set the honing angle to 1 degree greater. Simple, with great results.

Very interesting. Will you be placing the final 3D files for download somewhere?

As per the "The Forest Service Ax Manual - one moving part", 17 to 21 dps is suggested for the bevel, wich is 34 to 42 deg inclusive.
However, an microbevel of 25 to 32 dps (50 to 64 inclusive) is recommended in addition. 

However, you are talking about hatchets, not axes. I should read more carefully.

Yes, I've read that page as well, but perhaps there may be some errors there?  Note RichColvin's Sharpening Handbook says axes are 20-35 inclusive, based on type/usage.  This is in agreement with other sources, including some notable vendors of high-end, non-racing style, axes.  I've also seen various videos on how to create an axe gauge, and for instance when they describe making it for 25 degrees, they mark it for 12.5 degrees per side.

It was measured on the bevel so that 42 is inclusive angle. When you read about axes and hatchets it commonly refers to 20-35 inclusive depending on type/usage, not per side, if I'm understanding it correctly.  I'm new to this also so open to instruction.

I spent some time with a hand file to thin down the cheek of the hatchet to be more similar to the other profiles I've seen, something which might actually fit into the above template, but judging by eye since I don't have the template. I cleaned up the hand filing a little bit freehand on the Tormek.  After that I went back to the axe jig and dropped the USB a couple turns and reground the edge.  It now measures about 42 degrees, and cuts paper.  Not quite yet at the recommended 20-35 degrees, but getting there.

I have 3 very old hatchets of different styles, acquired from relatives. One looks to be a roofing or construction hatchet since it has a hammer on one side.  It still fits into the jig though.

None have any visible bevel to match. All are a mess with crooked edges, all convex down to the "edge", all practically blunt.  I First tried to black marker the average edge and match it.  After I did that I measured the angle on the anglemaster and it was 60 degrees. It now had a point but would barely tear paper.  I've got quite a bit of work ahead. More to post as it unfolds.

I've read various resources.  Note to Rich Colvin. Looks like the axe page reference to the Forest Service axe manual has moved.  Perhaps this is it now:  https://www.fs.usda.gov/inside-fs/delivering-mission/deliver/one-moving-part-forest-service-ax-manual