[Mike Soukup]

rbayer & nwagers are correct, try to avoid dead reconing whenever possible. Many FLL students figured this our the hard way because robots behave differently as the batteries drain. Motors slow down and you don't go as far in a given time interval as you'd like. So instead use the line, sense boxes using the retro-reflective tape, or use some other sensors. But try to avoid time based (or program loop counting) whenever possible.

[edit]
I forgot to mention another reason that dead reconing is bad. If a bin or robot is in the way, you won't go as fast as you will w/o objects in the way & therefore not as far in the time interval.
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Mike