"No Penalties For Missing A Class"

The rules at a particular university were such that if the
professor were not present in the classroom by 15 minutes past
the hour, the class was considered a "walk" and the students
were free to leave -- with no penalties for missing a class.
The rooms were equipped with the type wall clocks which
"jumped" ahead each minute, in a very noticeable fashion.
As it were, these clocks were also not of the most
sophisticated construction. Some enterprising student
discovered that if one were to hit the clock with chalkboard
erasers, it would cause the clock to "jump" ahead one minute.

So, it became almost daily practice for these students to take
target practice at the clock. (As fortune would have it, this
particular professor was not the most punctual, and the students
considered him severely "absent-minded"). A few well aimed
erasers, and lo, 15 minutes were passed, and class dismissed itself.

Well, when the day for the next exam rolled around, the professor
strolled into the room, passed out the exams, and told them
"You have one hour to complete."

The professor then proceeded to collect the erasers from around
the room, gleefully took aim at the clock. When he had
successfully "jumped" the clock forward one hour, he closed
the class and collected the exam papers.

Life does teach some lessons the hard way.