old_contents: UNITS = "SI"
  
  UNIT_LENGTH = 1
  UNIT_MASS   = 1
  UNIT_TIME   = 1
  
  DEFAULT_GRAVITATIONAL_CONSTANT  = 6.673e-11      # m3 kg-1 s-2          
  DEFAULT_SPEED_OF_LIGHT          = 299792458      # m s-1
  DEFAULT_SOLAR_MASS              = 1.98892e30     # kg
  DEFAULT_PARSEC                  = 3.08568025e16  # m
  DEFAULT_YEAR                    = 31556926       # s
  
  DEFAULT_h = 0.73
  
  G = GRAVITATIONAL_CONSTANT = DEFAULT_GRAVITATIONAL_CONSTANT
  c = SPEED_OF_LIGHT = DEFAULT_SPEED_OF_LIGHT
  
  def set_units(units):
      global UNITS
      global c, SPEED_OF_LIGHT, G, GRAVITATIONAL_CONSTANT
      
      if units=="SI":
          UNIT_LENGTH = 1
          UNIT_MASS = 1
          UNIT_TIME = 1
  
      elif units=="GALACTIC":
          UNIT_LENGTH = (1e6 * DEFAULT_PARSEC / DEFAULT_h)                # 1.0 Mpc h^-1
          UNIT_MASS = (1e10 * DEFAULT_SOLAR_MASS / DEFAULT_h)             # 10^10 M_solar h^-1
          UNIT_TIME = (1e3 * DEFAULT_PARSEC / DEFAULT_h)                  # 977.8 Gyr h^-1
      
      elif units=="CGI":
          UNIT_LENGTH = 0.01
          UNIT_MASS = 0.001
          UNIT_TIME = 1
  
      UNITS = units
      G = GRAVITATIONAL_CONSTANT = DEFAULT_GRAVITATIONAL_CONSTANT * UNIT_MASS * UNIT_TIME**2 / UNIT_LENGTH**3
      c = SPEED_OF_LIGHT = DEFAULT_SPEED_OF_LIGHT * UNIT_TIME / UNIT_LENGTH;
          
  set_units("SI")
new_contents: UNITS = "SI"
  
  UNIT_LENGTH = 1
  UNIT_MASS   = 1
  UNIT_TIME   = 1
  
  DEFAULT_GRAVITATIONAL_CONSTANT  = 6.673e-11      # m3 kg-1 s-2          
  DEFAULT_SPEED_OF_LIGHT          = 299792458      # m s-1
  DEFAULT_SOLAR_MASS              = 1.98892e30     # kg
  DEFAULT_PARSEC                  = 3.08568025e16  # m
  DEFAULT_YEAR                    = 31556926       # s
  
  DEFAULT_h = 0.73
  
  G = GRAVITATIONAL_CONSTANT = DEFAULT_GRAVITATIONAL_CONSTANT
  c = SPEED_OF_LIGHT = DEFAULT_SPEED_OF_LIGHT
  h = DEFAULT_h
  
  def set_h(new_h):
      global h
      h = new_h
      set_units(UNITS)
  
  def set_units(units):
      global UNITS
      global c, SPEED_OF_LIGHT, G, GRAVITATIONAL_CONSTANT
      
      if units=="SI":
          UNIT_LENGTH = 1
          UNIT_MASS = 1
          UNIT_TIME = 1
  
      elif units=="GALACTIC":
          UNIT_LENGTH = (1e6 * DEFAULT_PARSEC / h)                # 1.0 Mpc h^-1
          UNIT_MASS = (1e10 * DEFAULT_SOLAR_MASS / h)             # 10^10 M_solar h^-1
          UNIT_TIME = (1e3 * DEFAULT_PARSEC / h)                  # 977.8 Gyr h^-1
      
      elif units=="CGI":
          UNIT_LENGTH = 0.01
          UNIT_MASS = 0.001
          UNIT_TIME = 1
  
      UNITS = units
      G = GRAVITATIONAL_CONSTANT = DEFAULT_GRAVITATIONAL_CONSTANT * UNIT_MASS * UNIT_TIME**2 / UNIT_LENGTH**3
      c = SPEED_OF_LIGHT = DEFAULT_SPEED_OF_LIGHT * UNIT_TIME / UNIT_LENGTH;
          
  set_units("SI")
subject: Add ability to change h