Formula Sheets
Printable one-pagers of the key formulas behind each calculator — dense, scannable, ready for your desk.
Elapsed Time & Lap Splits
Core stopwatch identities: elapsed difference, paused totals, and lap splits at a glance.
Open sheet → UnitsUnit Conversion Factor Labels
Dimensional-analysis cheatsheet: convert through a base unit, cancel labels, and handle temperature offsets.
Open sheet → MathPercentage Triad
Three rearrangements of part, whole, and rate — plus percent change for growth and decline.
Open sheet → FitnessAdult BMI
Metric BMI identity, US customary conversion, and WHO adult category cutoffs used as a screening ratio — not a diagnosis.
Open sheet → OtherGPA and Weighted Grades
Letter-to-points on a 4.0 scale, credit-hour GPA, and a weighted course average from score × weight pairs.
Open sheet → Personal FinanceMortgage Payment
Standard amortizing payment, interest vs principal split, and remaining balance after k periods.
Open sheet → FinanceRule of 72
Doubling-time estimate for compound growth, with a reminder that it is an approximation best near mid-single-digit rates.
Open sheet → MathQuadratic Formula
Standard form, discriminant cases, and the ± quadratic formula for ax² + bx + c = 0.
Open sheet → MathSlope Between Two Points
Rise over run, undefined vertical lines, and the point-slope line through a known point.
Open sheet →