> math.eval('1 erg to joule')
{ [String: '1e-5 joule']
  units: [ { unit: [Object], prefix: [Object], power: 1 } ],
  dimensions: [ 1, 2, -2, 0, 0, 0, 0, 0, 0 ],
  value: 0.00001,
  fixPrefix: true,
  isUnitListSimplified: true }