## Martian Metrology.

In the Martian stories of Edgar Rice Burroughs (who also wrote the "Tarzan" stories) we come across a Martian set of units of measurement.

In my copy of "Thuvia, Maid of Mars" the following table is given:

10 sofads = | 1 ad |

200 sofads = | 1 haad |

100 haads = | 1 karad |

360 karads = | 1 circumference |

circumference = that of Mars at its Equator

We are also told, in the same book

1 sofad is about 1·17 Earth inches and the ad = 11·694 Earth inches

1 haad, or Barsoomian mile, contains about 2,338 Earth feet, and a karad is one degree.

In one of the later books a footnote tells us the **ad** is 9·75 feet and the **haad** 1,949·0592 feet - which contradicts what the other book tells us.

Comparing these values with the table it looks like there is an error in that table and that the later set of values are derived from the table and the radius of Mars.

Given that the mean radius of Mars is 11,118,766·4 feet and assuming that the value given for the ad is correct, what error has been made by the printer in the table?

(π = 3·14159265359 to 12 significant figures, and circumference of a circle is 2πr, where r is the radius of the circle.)

Source: a school Mathematics Worksheet of the 1970s