I’ve recently become aware of an issue at some National Rail stations, e.g. Stratford, Barking. These are stations where people will often arrive from outside the Oyster area on a paper ticket and wish to continue using their Oystercard without visiting the gateline. These stations sometimes have yellow standalone readers which record either entry or exit, often with a sign telling PAYG users to touch in here. You might not want to do this. If you are already touched in, either at that station’s gateline or because you are in the middle of a multi-mode journey, then touching in again could cause problems. You only need to use a yellow validator once at the beginning and once at the end of a journey. When interchanging within the same station you may need to touch on a pink route validator, but not a standalone yellow validator. Only when you interchange between two nearby stations (an out of station interchange) do you need to both touch out and touch back in again on yellow validators.