Mar 5, 2018 - 7:49 PM
in reply to acapote
"Zurich (zone 110) and Winterthur (zone 120) each count as two zones", my assumption is that it has to do with the price of the day pass. Since there's more public transportation in these zones, the price is likely to be higher.
If you're not planning to visit Winterthur you can just purchase the zone 110 day pass. If you're planning to go outside of the Zurich zone you will have to purchase that zone as well.
An alternative is the ZurichCARD. It is more expensive, but is has more benefits such as free transport in 2nd class by tram, bus, boat and cableways in all of Zurich and surrounding area, most of Zurich’s museums are for free, a 50% discount on the Zürich Old Town walking tour, 10 to 20% discount in selected shops in Zurich and a short cruise on Lake Zürich.