Batch percentage math, one pair per line. Modes: X% of Y · X is what % of Y · % change from X to Y (signed) · % difference (relative to the mean) · X increased by Y% · X decreased by Y%. The formula is printed above the results; rounding is half away from zero at the chosen number of decimals, computed without binary drift (1.005 → 1.01). Division by zero is reported per line. Everything runs locally.