MIG wrote:

This is a bit of a tangent, but if he had a zone 1 and 2 travelcard and
went from Heathrow to Stratford, touching in at Heathrow and out at
Stratford, would that count as one or two PAYG journeys, given that it
was split by the travelcard valid part?

(And I don't think there is any way of avoiding a zone 1 and/or 2
section without touching out and getting a bus, or maybe Silverlink.)

Single z3-z6 costs £1.80 on-peak or £1 off-peak.
Single z3 only costs £1 at all times.
Single z6-z3 via z1 costs £3.50 on-peak or £2 off-peak.

So off-peak the passenger would be charged £2, irrespective of how the
fare is calculated.

On-peak, the passenger would be charged £2.80 for 2 journeys plus
travelcard, or £3.50 for one journey.

I'm 90% sure that Oyster will give the on-peak passenger the most
favourable fare - ie 2 PAYG journeys plus travelcard - but haven't
tried it so can't confirm.

--
John Band
john at johnband dot org
www.johnband.org