On 20 Mar, 13:15, MIG wrote:
On Mar 20, 11:48*am, David Cantrell wrote:

On Thu, Mar 19, 2009 at 06:38:09AM +0000, Neil Williams wrote:
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.

You're buggered if there's the wrong type of leaves on the line though,
cos then rotations has only an approximate correspondence with distance
travelled.

That would only apply to powered axles, but skids could affect any of
them.

Surely it would only apply to axles where the wheelsets have brakes.
If a train 'skids', some or all of the wheels could lock up, not just
the powered ones. On modern stock, all wheelsets have brakes.