Great Oyster News

Aww yes ;D

However with oyster travelcards unresolved journeys don't actually do anything unless you get charged for going outside your zones [as I did once on the DLR]. So I fequently use my oyster card to open the gates onto the mainline platforms at Liverpool Street even though I have a paper ticket to Ilford because it's quicker than fiddling about trying to find said ticket in my pockets. Similarly, I get on at Mile End [with oyster], change platforms at Stratford, and go to Ilford and pay the excess fare there [when I'm running late for work]

You could do that but, AIUI you should (if you have a pay-as-you-go/pre-pay) touch out and then back in at Mile end and Barking. If you don't do that and your card was checked between Barking and East Ham then you would need to pay an excess/penalty fare for zone 4. If you do touch out then you would be charged (I presume) for a Z3 to Z2 single, a Z2 to Z4 single, then a Z4 to Z2 via Z1 single, unless the total of these is greater than Z1-4 travel card, in which case you would be charged that amount (I think thats how it works).

A couple of some questions of my own
At Ealing Broadway I touch in using the point on the DR platforms but take the Central Line, would my card be valid?
Would I be charged for touching on the DR platforms and then touching out on the Central platforms (assuming I have not touched out/in anywhere else in between, and do so quicker than I could get to NHG and back)?
Prseumably you are not charged for tapping in and out at the same station if you decide not to travel?
From Ealing Broadway to NHG, I would presumably get charged only for Z3 to Z2 if I used the Central Line, but Z3 to Z1 using the DR (as HSK is in Zone 1 only).
I went from KXSP to Royal Oak, spent some time on the platforms photographing trains going to/from Paddington and then carried on westwards to Hammersmith. Should I have touched out and then back in at Royal Oak? (Including the time at Royal Oak the KXSP to Hammersmith journey took less than 2 hours)
Is a journey from Queens Park -> Paddington (Bakerloo) -> Paddington (H&C) -> Hammersmith (H&C) -> Hammersmith (DR/PIc) -> Stamford Brook charged as one journey or three?

Ok, let's go back in time...........to when I worked in the ticket office...........just blowing the dust off my memory............

Your journey is not logical - that is in the sense that 99.9% of people would leave the system at Barking, do what they went there to do, then re-enter the system and travel to Hammersmith. It is also illogical from the point of view that Stratford to Hammersmith via Barking is not a 'direct' journey.

Though you may be able to that in less that two hours, you'd still get an unresolved journey as the Oyster system will know that you took too long travelling from Stratford to Hammersmith. The net result is a visit to the ticket office to have the unresolved journey sorted. You'll save a lot of hassle for yourself and the ticket office staff by simply touching your card twice at Barking!!

All readers at any one station will only register a 'touch' at the said station. The precise location of each reader within a given station is irrelevant.

There is a set time limit - if you touch in, then touch out at the same station within that time limit, you will not be charged. If you exceed the set time limit, you will have an unresolved journey.

Oyster will assume you have taken the most direct route, ie using the central line. If you go via HSK and the journey takes too long, you'll get an unresolved journey as per Joe s above. Should a revenue inspector find you on a train at HSK with a travelcard not having zone1 on it..........

Yes, you should have touched out, then in at the start of your second part of the journey. If you'd spent too long at Royal Oak, you'd end up with an unresolved journey as Oyster would think you'd taken too long to travel from Kings Cross to Hammersmith.

One journey.
This is an interesting example as you'll encounter barriers at both the Hammersmith stations - but Oyster knows you have made a logical direct journey between two points.

As you all may see from the above, Oyster has it's faults and can be less than perfect - but it can also be quite clever. Used correctly, it can be your friend ;D ;D