wrote in message
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No, because the wheels are not a fixed diameter, but get gradually
smaller as they are turned on lathes to remove flats and
imperfections. A small difference in diameter will lead to a large
cummulative error, if no corrections are made. There are other systems
which measure distance travelled (for example radar), but I don't know
how they are affected by different track formations etc.

I thought I heard that some lines work on revolutions, particularly the
Central Line.

If this is not the case, then how do Central line trains know where they
are?