Woodn't It Be Neat said:
I agree with the caliper comment - I can't see why one would want this tool? I'm hoping I'm attaching the picture correctly and if so you can see that there is an easy transfer of internal to external measurements built into the design of a standard caliper. It also creates depth measurement transfer as well. Can be inch, metric, or both, digital or vernier etc etc
If you look at Woodpecker's explanation of why both the mini and the standard version, that explains this as well.
The calipers use a very thin measuring surface; furthermore, that surface has the potential to "dig in" to soft materials like wood, and does not account for potential irregularities in the thicknesses of the material if something wasn't perfectly straight (or if it "warped" due to moisture or whatever after being formed).
These gauges being much wider should provide a better "average" over an area that should give a more useful metric when dealing with the softer material.
Calipers are really more optimal when working with metal. Nothing wrong with using them on wood, but there are times (even when using them on metal) when they will give the right answer to the wrong question if you aren't paying very close attention to what you are doing with them.
Another consequence of the thin blades on the caliper is the potential to angle them on the workpiece, which can also throw of the reading slightly. The wider surface of these gauges should also help to prevent that.
Furthermore, if you look at the inside measurement blades on the calipers, they are often too big to fit in something as small as a mortise, which the mini gauge was designed for.
That mini gauge would be very tempting if I didn't have a domino. Not as sure that the standard one would be as useful to me even then, though I can definitely see both as being of utility to some.