# Calculate Kollsman shift/ft versus setting/inHg
# Computationally efficient if, for any given instance
# of this class, the setting is not being changed often.
# Typical usage:
#  kxx = atmo.Kollsman.new();
#  kyy = atmo.Kollsman.new();
#  print (kxx.shift(29.92));	# calculates
#  print (kyy.shift(30.92));	# calculates
#  print (kxx.shift(29.92));	# uses cached value
#  print (kyy.shift(30.92));	# uses cached value

Kollsman = {
  new : func { { parents : [Kollsman] } },
  ft : nil,
  set : nil,
  shift : func(setting) {
    if (setting == me.set) {return me.ft}
    me.set = setting;
    me.ft = 145442.156 * (1 - math.exp(math.ln(me.set/29.921260) * 0.1902632365))
  }
};