Furthermore, the CIS▸ (and online National Rail departures) often show it as being 'On Time' right up until it is due. I've checked train progress on the National Rail website a few times and noticed that it has been showing 'on time' at Wokingham, while predicting 5 minutes late at earlier stations, including Crowthorne, so there is no possibility of recovery. Is there some problem in the interface between North Downs and Waterloo lines information systems that means late running on NS isn't picked up until the train is nearly at Wokingham?
Its nothing to do with the interface between
FGW▸ and
SWTs▸ information systems, they both run off of the same sources for information.
However the line towards Ash, has limited signalling and therefore if a train is delayed it may take slightly longer for the information system to pick up on this, as it will not know about it until it passes the next signal, this can be a few miles away so could take up to 5 minutes.
Furthermore this signal being a few miles away can mean that the information on how late the train actually is may be incorrect, as there is no way on telling the exact time it left the previous station or stations before the next signal it will reach. Although live departure boards may post departure times from stations on the North Downs route this may not be 100% accurate because of the reasons I just specified, so I would not rely on it.
It is also worth noting that the predictions on National Rail Departure boards do not communicate with the systems at stations, this is generally because information on this system, not just the predictions, but also the departure report that don't interface with Trust are known to be inaccurate, that being the reason why Trust does not take information for certain stations. The reason for your train being reported as being expected On time at Wokingham station and also online is because the system at SWT stations are linked to the online system and is assuming the train will arrive on-time because it is assuming it is at the point in the big signal sections that will make it on time, of course sometimes the train isn't and when it finally does pass the next signal the delay is updated.