code: def OD(ND):
      
      index = (np.abs(np.array(pipedb['NDinch']) - (ND))).argmin()
      return pipedb.iloc[index, 1]
docs: Return a pipe's outer diameter according to its nominal diameter.
  
      The pipe schedule is not required here because all of the pipes of a
      given nominal diameter have the same outer diameter.
  
      Steps:
      1. Find the index of the closest nominal diameter.
         (Should this be changed to find the next largest ND?)
      2. Take the values of the array, subtract the ND, take the absolute
         value, find the index of the minimium value.