How many times do calligraphy classes take place every six months?

Between 36 and 48 times. Calligraphy classes are held once or twice a week for half a year. The duration of a class ranges from 1 hour to 1.5 hour, and the number of classes in a semester ranges from 36 to 48 times. If you attend classes twice a week, 36 times is the lower limit, and if you attend classes only once a week, 48 times is the upper limit.