Function getExpressionScale

src/compute-engine/numerics/unit-data.ts:469–503

(expr: UnitExpression)

  }

  if (op === 'Power') {
    if (expr.length !== 3) return null;
    const d = getExpressionDimension(expr[1]);
    const exp = expr[2];
    if (!d || typeof exp !== 'number') return null;
    return d.map((v) => v * exp) as DimensionVector;
  }

  return null;
}

/**
 * Compute the scale factor for a MathJSON unit expression relative to
 * coherent SI.
 *
 * - If `expr` is a string, delegates to `getUnitScale`.
 * - `["Multiply", a, b, ...]` — multiplies scales.
 * - `["Divide", a, b]` — a.scale / b.scale.
 * - `["Power", base, exp]` — base.scale ^ exp.
 *
 * Returns `null` if any component is unrecognised.
 */
export function getExpressionScale(expr: UnitExpression): number | null {
  if (typeof expr === 'string') return getUnitScale(expr);

  if (!Array.isArray(expr) || expr.length < 2) return null;

  const op = expr[0];

  if (op === 'Multiply') {
    let result = 1;
    for (let i = 1; i < expr.length; i++) {
      const s = getExpressionScale(expr[i]);
      if (s === null) return null;
      result *= s;
    }
    return result;
  }