In message , Clive D. W. Feather
writes
In article , Steve Fitzgerald
] writes
Because they are "If you brake /now/ then this is the number of cars
that will be at the platform when you stop".

No they're not. Not on the Picc at least, they indicate how many cars
you are out so that you know whether to brake or not. They are all
the same distance apart and the 6 car mark is exactly a train length
out of the platform.

Other lines may vary but I don't think they do as that's what's in our
training.

The ones on the Northern Line definitely vary. Southbound out of East
Finchley (steep downhill) they almost touch each other.

Then they are wrong. I've only today read an item on the Union notice
board about this and my theory was correct. There is about to be a
campaign commenced to correct these and other known anomalies.

I've also received these responses from a couple of colleagues who work
on the Northern in answer to a query I posed them:

They should be at equal distances apart and equal to how many cars out
of the platform the train is. However, they do not always start from
the end of the platform, e.g. where the platform is longer than normal.
I can't remember the postilions of the marks at East Finchley off hand.
It may be they begin from the stopping mark in some cases.

and

IIRC (having had a couple of "days on the road" on the black line last
year) there are some locations where count-up markers 1 to 6 are
correctly spaced for 1995 stock, but a count-up marker 7 (for 1959
stock) remains in position. As 1995 stock has longer cars (which
allowed a 6-car train to replace a 7-car train of the older stock on a
like-for-like basis), it follows that the 7 marker is only just beyond
the 6 marker.

To the uninitiated, this may give the misleading impression the gaps
between each marker gradually diminish as you depart the platform - if
true, this would be consistent with (and lead to the assumption that)
the markers being spaced according to braking points. But they're not
spaced that way - markers 1 to 6 are all equally spaced, to correctly
indicate the position of a stationary train.
--
Steve Fitzgerald has now left the building.
You will find him in London's Docklands, E16, UK
(please use the reply to address for email)