Hi, could someone please explain a little about the 特码玄机诗? What is it meant for and who writes the verses?

I found the verse "游山玩水得佳人 二七争开九得利" in my calendar and I do understand the characters but I have no idea what they mean all together? I would be really grateful if someone would explain what that is all about or at least gave me a link to read more about it, the link can be Chinese too.

Thank you!