[dragnet2]

Interesting that the tires or roller tracks or whatever the term is have the two different types of tread

Interesting you should ask.

Each wheel has a pattern which helps it maintain traction but also leaves patterned tracks in the sandy surface of Mars. That pattern is used by on-board cameras to judge the distance traveled. The pattern itself is Morse code for "JPL" (·--- ·--· ·-··) JPL: Jet Propulsion Laboratory

[steve86]

That pattern is used by on-board cameras to judge the distance traveled

Why don't they use GPS?

just kidding