code: def unit_conversion(current, desired):
      
      current = str(current).strip().lower()
      desired = str(desired).strip().lower()
      conversion = TO_INCH[current] / TO_INCH[desired]
      return conversion
docs: Calculate the conversion from one set of units to another.
  
      Parameters
      ---------
      current : str
          Unit system values are in now (eg 'millimeters')
      desired : str
          Unit system we'd like values in (eg 'inches')
  
      Returns
      ---------
      conversion : float
          Number to multiply by to put values into desired units