Do I have to punch in every time I go to Berlin or only once when I use it for the first time that day?

As long as you punch in after 3 am, a single-day ticket can take the subway, suburban railway, bus, tram and ferry unlimited times in the designated charging area, and can be used until 3 am the next day.

There are three kinds of one-way tickets: AB, BC and ABC. You can take a bus in the designated toll area within two hours after the ticket is issued, and you can change to subway, bus and tram on the way. There is no limit on the number of times, but you can't go back to the ticket office by train.

Extended data:

Berlin station usually has a tourist welcome card, with 48-hour tickets, 72-hour tickets, 3-day tickets, 5-day tickets and 7-day tickets to choose from. With the ticket, you can take the local bus, tram, light rail (S-Bahn), subway (U-Bahn) and short-distance train (RE, RB).

If you are a student studying in Germany, you can usually get a semester ticket, which is included in the registration fee, equivalent to a monthly ticket for half a year, which is cheaper than the normal price.

Promissory notes cover cities and surrounding areas, and may also cover the whole state. As long as you don't leave the state, you can take all public transportation except high-speed rail (ic and ICE).