You’re right. Sofs, sofads, ads, haads, and karads are mentioned at the bottom, but I can’t find the distance measure they correspond to. We can’t use the circumference of Mars as calculated from Earth, since the distances ERB gives of Barsoom are slightly different. But we know the following from a footnote at the end of Chapter 6 of Thuvia, Maid of Mars:
- 360 karads = 1 circumference of Mars at equator
Since Francesca Baerald’s Map contains 18 units of measure on each hemisphere of Barsoom, each of those measures must be equivalent to 10 karads
