NOTCHES:
A notch from hub doubling is the product of overlapping parts of a device that drop off in relation to one another. Notches are most often seen at corners and with serifs.
Now for example if a die shows hub doubling and there is a geographic shift in relation to the rotation (north, south, east or west), the notches will be more apparent. The proceeding illustration shows a CCW rotation with the Red being the first hubbing and the Green the second - the green is also slightly south (or down in relation to the red). While the spread is minor, the notches are obvious as the drop offs are throughout much of the doubling. Even the round parts (like the o and S) show an ellipse that ever so gently comes inward as opposed to straight lines that would be seen with MD.
Now we will see a stronger CCW spread that does not show a significant geographic change in position, the result is fewer notches, but where the design drops off, such as the serifs on the S or the top of the A, there will be minor notching or splits seen.
Next is some notching diagrams to give one an idea of where (and the variety of places) Class I (and also Class V) hub doubling can produce notches.
Below is a nice Class I DDO, listed as
1941P DDO-002. You can see strong rounded doubling and separation lines on all devices - strongest in IGWT, but the notching is harder to perceive.
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