Dear Ben,
The Sept
Severus rev looked oval at first, but now that I measure the
circle I get – on the photo - 62mm x 63mm, so perhaps a slight tilt of the coin during photography. The other was the
Probus FIDES, where only a small
part of the
circle is visible, to the right, and it looks too straight. Maybe just an artefact, maybe a scratch on the die not a compass
circle, who knows.
After going through the coins figured here I am in fact even more convinced that a compass was used. The main purpose would be to mark the size and position of the pearl
border. And clearly it was not uncommon to add one or more circles to indicate the space for the
legend.
One might note that all examples except mine are of silver coins. In bronze, the surface in only rarely preserved well enough for the preservation of weak features like this.
All in all, a small piece of information about how the engravers worked. Neat.
/Lars