Egoyomi (盲暦) is a Japanese picture calendar, in which the length and order of the months are deducible, like a code, from cryptic markings that are incomprehensible to most people but transparent to enthusiasts.
[1] These type of calendars thrived during the so-called Meiwa era of the late 18th century.
However, the extent to which these pictures misled the authorities is a topic of debate.
Eventually, the same pictures reached the public market: the calendar information was carved off the wooden blocks, which were then reprinted and sold.
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