Math. Piece of cake. I did well in math until I hit Algebra. All but flunked that. Teacher offered me a passing grade so long as I didn't take Geometry. Years later, due to needing more math to advance I took a crash course in Geometry and Trig. I first brushed up with Advanced math before. I passed with flying colors. I thought Geo. and Trig. easier the Algebra. From there, for shop stuff, it was just learning formulas. Now, the kicker is after all those classes I never once used any of it in the shop I didn't have to. It's all worked out with computers and machines now.
First, Fractions are a piece of cake. What's half of 1/8? Simple, 1/16. What's half of 7/64? Again simple, 7/128. All you do is double the dominator. What's one fourth of 3/16? 3/64. All you do is double the dominator twice.
Those GPS thingies. Same difference as in finding location of a bore or drilled or a tapped hole in a transmission case or engine block. GPS units work off coordinates established on a larger scale and some times referred to as triangulation. The formula isn't much different. For bore location; The square root of X squared plus y squared times 2 equals "you are here."