When you swipe your card, you charge two yuan in advance, and then deduct the money according to the time, but the machine often doesn't need money, that is, it never takes the number after swiping the card. In fact, it doesn't matter if you deduct the money, because the money is deducted from the utility bill. For example, four people in the dormitory spend * * copies of water and electricity in 50 yuan a month, and four people spend * * 10 yuan on shower cards. In this case, the water and electricity fee paid by each person is (50- 10)/4 = 10 yuan, so it makes no difference whether the money is deducted or not.