When I started the first page of Spherical Astronmy by Robin M Green, I realized I couldn’t remember any of my high school math. Wow, I remember being so good at math! I took AP Calculus in high school and know can’t remember what a cosine is.
So, I searched around Amazon and found a great series of books called Master Math by Debra Anne Ross. I got the books on Basic Math & Pre-Algebra, Algebra, Geometry and Trigonometry. I started reading them with the intent of reading the entire books. But, after a while, I realized that most of this I would probably forget again and I didn’t know which parts applied to astronomy. So, I ended up skimming them. 
I also got one of other books called Precalculus Mathematics in a Nutshell by George F. Simmons. Though the book was really short, it was really to the point and made for a nice summary. This will provide a good basis for my work on the Astronomy Calculator.
