Problem description:

1. If the radius of the sundial disk remains the same, how to determine the length of the sundial needle?

2. If the metal pointer of the sundial is long, how to remedy it (without changing the pointer length and the radius of the sundial disk)?

Analysis:

Let the angle between the dial and the horizontal plane be θ, the radius of the dial be r, and the length of the dial be l 。

L = r * ctgθ。

This formula also solves problem 2. If the metal pointer is too long, flatten the sundial so that CTG θ = L/R. 。