TfL took over have been fitted with standalone Oyster card readers similar to those at ungated Underground and DLR stations. The validators at which were needed to enter/exit the Oyster card system when changing to and from the Victoria line were replaced with route validators, coloured pink: these are used to show that a traveller using Oyster PAYG changed lines at that station, showing which of the possible routes was used. Typically, this avoids paying for zone 1 when the passenger did not travel into it. Ticket stock is common National Rail stock, as Overground services remain part of the National Rail network, but sometimes with a large TfL roundel in the centre and the repeated legend "Rail Settlement Plan" or on newer versions "National Rail" on a light green background. This ticket stock, coded "TFL" on the reverse, was introduced in November 2007. Ticket pricing Oyster PAYG is charged on the same zone-based rules as for the Underground and the Docklands Light Railway. Stations outside Greater London (except Watford Junction) are included in the new Travelcard Zones 7-9. On 2 January 2008 Acton Central was moved from zone 2 to 3, Hampstead Heath from 3 to 2 and Willesden Junction from 3 to both 2 and 3. Paper tickets are charged on the same zone-based rules as for Underground and DLR paper tickets, which were expanded to take in the extra zones covered. Watford Junction has its own fare scale. Paper tickets are significantly more expensive than using Oyster PAYG. Performance Although a TfL service, the Overground is part of the National Rail network, unlike the Underground. The most recent figures released by Network Rail (NR), for period 7 (20132014), showed that it had achieved 96.6% of the Public Performance Measure (PPM) target for punctuality and reliability set by the ORR – down 0.9 percentage points on the period last year. The moving annual average (MAA) of the PPM for the 12 months to 12 October 2013 was 96.5%. TfL, in conjunction with the Massachusetts Institute of Technology, has investigated the use of data from the Oyster smartcard ticketing system to measure the performance of the Overground explicitly from the passenger perspective. In the autumn 2011 National Passenger Survey, conducted by Passenger Focus, London Overground received an overall satisfaction rating of 92%, a 7% improvement on the previous survey. However, a survey in February 2014 by the consumer group