I am blogging from Caltrain right now. For this month I have a Zone 1-3 pass, this is my first ride of the month. Due to poor system design, I am supposed to tag on/off for this ride, exactly from zone 1-3 or 3-1. If I don't tag - citation. If I get off at BART and tag off at zone 2, I pay $4.50 to ride less than the pass I own allows, and my pass is still not activated.
This is asinine. To explore the algorithm the lovelies at Clipper designed, I decided to try an experiment. At Sunnyvale, in zone 3, I tagged on. $8.50 - the fare to Gilroy, was deducted. Then I tagged off - this should annul my trip and it did, refunding my $8.50. The question is - was my pass activated (probably not). I do know that the pass had been "loaded" - I had seen that on a ride last month (why not just activate it?).
I got on the train and found a conductor to ask if my pass was valid. He tagged my card and it said "YES ZONE 3 - ZONE 3".???
It did not say monthly.
I'm hazarding a guess that there is a bug that would allow you to tag on, annul the trip, and ride in the same zone.
I got off in Mountain View and tagged again.