I guess we have better measurements on the star distances than we did when the book was published (2002) - however even the estimated distances still have large margins of error (+/-
| 10%).
It looks like Brophy took Vega as his reference (Vega's distance/speed is accurately known) and calculated the others based on this measurement.
| error, it's difficult to say whether the stones accurately represent the star distances, because there is no accuracy to begin with. I had assumed modern astronomy could tell the