text: """Define unit system for pax (i.e., seconds, etc.)
  This sets up variables for the various unit abbreviations, ensuring we always
  have a 'consistent' unit system.  There are almost no cases that you should
  change this without talking with a maintainer.
  """
  
  from __future__ import division
  
  # From physics.nist.gov, January 2015
  electron_charge_SI = 1.602176565 * 10 ** (-19)
  boltzmannConstant_SI = 1.3806488 * 10 ** (-23)
  
  m = 10 ** 2  # distances in cm
  s = 10 ** 9  # times in ns
  eV = 1  # energies in eV
  C = 1 / electron_charge_SI  # Charge in # electrons, so voltage in Volts
  K = 1  # Temperature in Kelvins
  
  # derived units
  Hz = 1 / s
  J = eV / electron_charge_SI
  kg = J * s ** 2 / m ** 2
  V = J / C
  A = C / s
  N = J / m
  Pa = N / m ** 2
  bar = 10 ** 5 * Pa
  Ohm = V / A
  
  # 10 ^ -3 base units
  mm = 10 ** (-3) * m
  ms = 10 ** (-3) * s
  mK = 10 ** (-3) * K
  mC = 10 ** (-3) * C
  meV = 10 ** (-3) * eV
  
  mHz = 10 ** (-3) * Hz
  mJ = 10 ** (-3) * J
  g = 10 ** (-3) * kg
  mV = 10 ** (-3) * V
  mA = 10 ** (-3) * A
  mN = 10 ** (-3) * N
  mPa = 10 ** (-3) * Pa
  mbar = 10 ** (-3) * bar
  mOhm = 10 ** (-3) * Ohm
  
  # 10 ^ -6 base units
  um = 10 ** (-6) * m
  us = 10 ** (-6) * s
  uK = 10 ** (-6) * K
  uC = 10 ** (-6) * C
  ueV = 10 ** (-6) * eV
  
  uHz = 10 ** (-6) * Hz
  uJ = 10 ** (-6) * J
  mg = 10 ** (-6) * kg
  uV = 10 ** (-6) * V
  uA = 10 ** (-6) * A
  uN = 10 ** (-6) * N
  uPa = 10 ** (-6) * Pa
  ubar = 10 ** (-6) * bar
  uOhm = 10 ** (-6) * Ohm
  
  # 10 ^ -9 base units
  nm = 10 ** (-9) * m
  ns = 10 ** (-9) * s
  nK = 10 ** (-9) * K
  nC = 10 ** (-9) * C
  neV = 10 ** (-9) * eV
  
  nHz = 10 ** (-9) * Hz
  nJ = 10 ** (-9) * J
  ug = 10 ** (-9) * kg
  nV = 10 ** (-9) * V
  nA = 10 ** (-9) * A
  nN = 10 ** (-9) * N
  nPa = 10 ** (-9) * Pa
  nbar = 10 ** (-9) * bar
  nOhm = 10 ** (-9) * Ohm
  
  # 10 ^ 3 base units
  km = 10 ** 3 * m
  ks = 10 ** 3 * s
  kK = 10 ** 3 * K
  kC = 10 ** 3 * C
  keV = 10 ** 3 * eV
  
  kHz = 10 ** 3 * Hz
  kJ = 10 ** 3 * J
  Mg = 10 ** 3 * kg
  kV = 10 ** 3 * V
  kA = 10 ** 3 * A
  kN = 10 ** 3 * N
  kOhm = 10 ** 3 * Ohm
  kbar = 10 ** 3 * bar
  kPa = 10 ** 3 * Pa
  
  
  # 10 ^ 6 base units
  Mm = 10 ** 6 * m
  Ms = 10 ** 6 * s
  MK = 10 ** 6 * K
  MC = 10 ** 6 * C
  MeV = 10 ** 6 * eV
  
  MHz = 10 ** 6 * Hz
  MJ = 10 ** 6 * J
  Gg = 10 ** 6 * kg
  MV = 10 ** 6 * V
  MA = 10 ** 6 * A
  MN = 10 ** 6 * N
  MOhm = 10 ** 6 * Ohm
  Mbar = 10 ** 6 * bar
  MPa = 10 ** 6 * Pa
  
  
  # 10 ^ 9 base units
  Gm = 10 ** 9 * m
  Gs = 10 ** 9 * s
  GK = 10 ** 9 * K
  GC = 10 ** 9 * C
  GeV = 10 ** 9 * eV
  
  GHz = 10 ** 9 * Hz
  GJ = 10 ** 9 * J
  GV = 10 ** 9 * V
  GA = 10 ** 9 * A
  GN = 10 ** 9 * N
  GOhm = 10 ** 9 * Ohm
  Gbar = 10 ** 9 * bar
  GPa = 10 ** 9 * Pa
  
  # other units
  cm = 10 ** (-2) * m
  ng = 10 ** (-12) * kg
  # Townsend (unit for reduced electric field)
  Td = 10 ** (-17) * V / cm ** 2  # noqa
  
  electron_charge = electron_charge_SI * C
  boltzmannConstant = boltzmannConstant_SI * J / K