Thanks for that post — that's interesting, and explains a considerable bit. I ride CalTrain often, but their readers are bolted to the concrete… I'm surprised they're not updated more frequently? (Even the CalTrain operators say to give a week.)

The whole "tag on/off once at the beginning of the month" (which I've always thought was the weirdest thing…) then is to sync the on-card value w/ what you own I suppose, so that it scans properly on their readers. Now I wonder that given that I buy from Walgreens, if that's an absolute necessity, or a hardship imposed by people being too lazy to explain the inner workings of the card; it's a pain b/c if you forget to tag off, you get charged full-fare (and your monthly pass is deactivated until you re-add value to the card…), as I'd much rather just buy the monthly pass and not have to do the monthly tag dance.