Rule of twelfths
The rule of twelfths is a memorable way to approximate a sinusoidal curve by twelve equally-spaced line segments of slope
¹⁄₁₂, ²⁄₁₂, ³⁄₁₂, ³⁄₁₂, ²⁄₁₂, ¹⁄₁₂, ⁻¹⁄₁₂, ⁻²⁄₁₂, ⁻³⁄₁₂, ⁻³⁄₁₂, ⁻²⁄₁₂, and ⁻¹⁄₁₂
respectively. It rounds but otherwise uses exact values along the curve.
I learned about the rule of twelfths from a kayaking instructor and guide, who used it to estimate the tides. In locations and seasons with a semidiurnal tide pattern, the period of the tide is roughly 12 hours so the rule of twelfths tells you what the water will be doing in each hour.