The Fundamentals of Agriculture

In a post-apocalyptic world, how could you work out what day of the year it is in an unknown time into the future? I.e., how could you reconstruct the calendar from first principles? How can you pinpoint where you're on the earth and track your progress through the seasons across the year? These are some of the most fundamental challenges that civilization has been solving over centuries and millennia. The gateway technology you want to get to is the printing press. In our own history, if you want to copy a document, if you wants to share an idea across the whole population, the only way of doing that is filling a room full of people like this. It's incredibly labor