What does "CORRECTION" mean?

I was looking a Jubilee Line train platform indicator in Canada Water yesterday and it comes up with just


and then seemed to return to the state it was showing before (next train to North Greenwich and then three more to Stratford)

I was wondering what the nature of the correction might be? I think I might have seen something similar on the Northern Line a long, long time ago. But at least that makes sense, the Northern Line has three northern-end destinations and a choice of to pass thought the city or west end.

But I’m sure I’ve never seen anything in the feeds with a CORRECTION . Not even the scary-sounding GIGO “Check destination on the front of the train”.

Hi @briantist

I see this at North Greenwich too.

I’m not sure, but I think that every time the order changes, it issues it as a correction. Very vidiprinter-esque.


I’m not sure the trains can charge order on the Jubilee line. I think I’ve also heard the PA at the station tell me the wrong thing about the line status (“Stratford is closed, the DLR isn’t working between Canning Town and Stratford International”) when there was a Good service everywhere.

But I’m also convinced this this sign at Barking has shown the same thing on it every time I’ve been there (the time changes)

But when I check the TfL website it says https://tfl.gov.uk/tube/stop/940GZZLUBKG/barking-underground-station

the data seems to be missing here too…

‘Correction’ is generated by the sign, as opposed to being sent to it. It means something in the data sent to the sign has changed, but it might be something that doesn’t affect the sign display. it could be a train number change, or maybe the comms link to the sign went down and came up again?

1 Like

@netstruggler I don’t know what the protocol is between the signs and control for them.

I’m guessing that it’s like the iBus signs, in that they are sent the list of destinations and their arrival times and the sign uses that to work out the order and to show the integer minutes to the arrival of the service.

It’s possible that the signs are getting updated timings for the arrivals (in Unix seconds) and whilst the change isn’t causing the number of minutes for the service to display differently, “CORRECTION” is showing up because one of the trains is actually going to arrive 28 seconds later.

Anyway, it’s not great customer communications, but none of those era signs are.

If memory services they are/were being made by https://www.hanoverdisplays.com/

The signs across the network are a complete hotch-potch of technologies. I believe on the Jubilee they use a message protocol developed in the 1980s, originally sent over serial, now using Ethernet.

The arrival list contains a unique ID number, a destination and an arrival time in minutes for each train in the list. Generally it’s the ID number that changes, either due to a genuine edit or some sort of unintended refresh, which triggers a CORRECTION message but an unchanged display.


Ah yes, the old Terminal Server being used in reverse mode trick, I remember doing lots of that! It was a common solution to problems back in the 1990s. People used to be amazed by my serial port sniffing skills.!

I think I’m going to have to write some code on the old TrackerNet to see if I can find the “ID number” and build myself a emulation in CSS…