Numerals on Panerai dials......

Q: Why is the Arabic numeral “6” different from one Pam to another?

A: The simple/short answer, with only a few exceptions, is that the “open 6” is representative of Historical Pams [112, 111, et al], whereas the “closed 6” is representative of Contemporary Pams [104, 123 et al].

Furthermore, the Historicals are open, we presume, because of the early usage of the sandwich dial that had actual "cut outs" to allow the luminous material to be visible. The 113 and other white dials are one exception to the Historical/Contemporary rule—there is not historical precedence for a white dial, and therefore we presume they all use the “closed 6.”