I have read Florian Cajori's book "A history of mathematical notations."
Cajori explained about several symbols for unknown. Rudolff used weird symbols.
I could identify some symbols: "z" for zensus, "c" with a loop for cubus, "eszett ß" for sursolidum.
But, I could not understand the symbol for radix. It looks like conjunction of "2" and "e".
Could you teach me which letter was used for radix?