Paul Bouchier of the Dallas Personal Robotics Group has posted a new article, A Quick & Easy Guide to Calibrating Your Robot Using UMBmark, to help explain how the Borenstein UMBmark can be used to help diagnose and improve dead reckoning in your robot. Borenstein's paper, UMBMark - A Method for Measuring, Comparing, and Correcting Dead-reckoning Errors in Mobile Robots (PDF format) was originally published back in 1994 and has been in use by both professional and hobby roboticists around the world since. The basic idea is that most dead-reckoning errors come from either systematic errors such unequal wheel diameters or non-systematic errors such as wheel-slippage. The UMBmark test is designed to uncover the systematic error in a way that make the cause more obvious to the builder. The best part is that the UMBmark is easy to do and require no fancy test equipment. The video above is DPRG member David P Anderson's JBot performing part of the UMBmark during a 2007 DPRG UMBmark exercise