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Here is a course about learning to calculate the calendar mentally without external aids. It's a nice and lightweight algorithm that is easy to use and is easy in the brain.
It can help you learn Spanish too since it also has video and audio both in Spanish with which you can compare between your hearing, the actual text and its actual pronounciation.
This is the index of the minicourse:
It's possible that there will be more videos for this course in the future, so to know if there are more, just refer to the URL of the index of the course. In the future there should be an index HTML page showing the full index of videos and resources.