old_contents: from __future__ import division, print_function, unicode_literals
  
  import numpy as np
  
  import scipy.constants as const
  
  N_A  = const.N_A
  A_Be = 9.012182 # g / mol Be
  
  def N10(R10to9, Mq, Mc, n10b=0.0, unc_R10to9=0.0, unc_Mc=0.0, unc_n10b=0.0):
      
      N10 = ((R10to9 * Mc * N_A / A_Be) - n10b) / Mq
      
      # standard error propagation
      # we assume error in quartz measurement is so small as to not matter
      A = unc_R10to9 / Mq * (Mc * N_A / A_Be)
      B = unc_Mc / Mq * (R10to9 * N_A / A_Be)
      C = unc_n10b * -1 / Mq
      unc_N10 = np.sqrt(A**2 + B**2 + C**2)
      
      return (N10, unc_N10)
  
new_contents: from __future__ import division, print_function, unicode_literals
  
  import numpy as np
  
  import scipy.constants as const
  
  N_A  = const.N_A
  A_Be = 9.012182 # g / mol Be
  
  def N10(R10to9, Mq, Mc, n10b=0.0, unc_R10to9=0.0, unc_Mc=0.0, unc_n10b=0.0):
      
      N10 = ((R10to9 * Mc * N_A / A_Be) - n10b) / Mq
      
      # standard error propagation
      # we assume error in quartz weighing is so small as to not matter
      A = unc_R10to9 / Mq * (Mc * N_A / A_Be)
      B = unc_Mc / Mq * (R10to9 * N_A / A_Be)
      C = unc_n10b * -1 / Mq
      unc_N10 = np.sqrt(A**2 + B**2 + C**2)
      
      return (N10, unc_N10)
  
subject: clarify comment