London Banter - View Single Post

Neil Williams · March 19th 09, 05:38 AM posted to uk.railway,uk.transport.london

On Wed, 18 Mar 2009 16:17:22 -0700 (PDT), wrote:

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.

A more clever system could use the GPS data to derive how far the
train travels on one revolution on that day and use it later when the
GPS was not available.

OTOH, the Mk1 eyeball would also do the job, though I hear that there
was an incident of it failing to do so at Bletchley last week.
Fortunately, the Mk1 eyeball of the passengers prevailed, and (as one
would expect) nobody fell out.

Neil

--
Neil Williams
Put my first name before the at to reply.