alex_t wrote:

One day Travelcard Z1-6 is also valid on National Rail, so it covers
most of your way already. So from £14.50 you pay for the Travelcard
(most of the amount) + rail ticket from boundary of Z6 to
Sawbridgeworth.

That is right, but this can also lead to not very clear oddities, the
really interesting things begin when buying return tickets from stations
just outside Z6 to a station in the zones, but with quite a distance
from where you enter Z6. Take for example Dartford to Crystal Palace, a
SDR costs £16.00 and a Peak Day Travelcard £15.70 or Watford High Street
to Greenwich where a SDR is £16.60 and a PDT £15.20.

Of course a Peak Day Travelcard for Z1-6 costs £13.20 in all cases and
the oddities occur in cases where a Standard Day Return for the whole
journey is more than £13.20 expensive than a Standard Day Return to the
Z6 boundary. I would strongly recommend people who are buying return
tickets from a station near the Z6 boundary to a station within the
zones to look up prices for travelcards too since they may be cheaper,
especially for peak hour tickets.

--
Olof Lagerkvist
ICQ: 724451
Web: http://here.is/olof