Function convertCompoundUnit

src/compute-engine/numerics/unit-data.ts:641–661

(
  value: number,
  fromUnit: UnitExpression,
  toUnit: UnitExpression
)

    }

    for (const sym of members) {
      if (sym === rep) continue;
      const e = result.get(sym)!;
      const s = getUnitScale(sym)!;
      magnitudeScale *= (s / repScale) ** e;
      result.set(rep, result.get(rep)! + e);
      result.delete(sym);
    }
    if (result.get(rep) === 0) result.delete(rep);
  }

  return { factors: result, magnitudeScale };
}

/**
 * Rebuild a canonical `UnitExpression` from a factor map (symbol → exponent).
 *
 * Numerator factors (positive exponents) become a bare symbol, a `Power`, or
 * a `Multiply`; denominator factors (negative exponents) go under a `Divide`.
 * When there are only denominator factors, negative `Power` forms are emitted
 * directly (matching what `quantityDivide`'s scalar/Quantity path produces),
 * since a numeric `1` is not a valid unit symbol.
 *
 * Returns `null` for an empty map (fully cancelled → dimensionless).