old_contents: # Calculate the distance to an object of known size.
  # We need to know the perceived focal length for this to work.
  #
  # Known Focal Length values for calibrated cameras
  #   Logitech C920:              H620 V?
  #   Microsoft Lifecam HD-3000:  H652 V?
  #
  class TriangleSimilarityDistanceCalculator:
      knownSize = 0
      focalLength = 0;
  
      def __init__(self, knownSize, perceivedFocalLength = None):
          self.knownSize = knownSize
          self.focalLength = perceivedFocalLength
  
      # Call this to calibrate a camera and then use the calibrated focalLength value
      # when using this class to calculate real distances.
      def CalculatePerceivedFOVAtGivenDistance(self, perceivedSize, distance):
          focalLength = perceivedSize * distance / float(self.knownSize)
          return focalLength
  
      # This will return the real world distance of the known object.
      def CalcualteDistance(self, perceivedSize):
          if self.focalLength == None:
              raise ValueError("Did you forget to calibrate this camera and set the perceived focal length?")
          distance = self.knownSize * self.focalLength / float(perceivedSize)
          return distance
  
new_contents: # Calculate the distance to an object of known size.
  # We need to know the perceived focal length for this to work.
  #
  # Known Focal Length values for calibrated cameras
  #   Logitech C920:              H622 V625
  #   Microsoft Lifecam HD-3000:  H652 V?
  #
  
  PFL_H_C920 = 622
  PFL_V_C920 = 625
  PFL_H_LC3000 = 652
  PFL_V_LC3000 = 652
  
  class TriangleSimilarityDistanceCalculator:
      knownSize = 0
      focalLength = 0;
  
      def __init__(self, knownSize, perceivedFocalLength = None):
          self.knownSize = knownSize
          self.focalLength = perceivedFocalLength
  
      # Call this to calibrate a camera and then use the calibrated focalLength value
      # when using this class to calculate real distances.
      def CalculatePerceivedFocalLengthAtGivenDistance(self, perceivedSize, knownDistance):
          focalLength = perceivedSize * knownDistance / float(self.knownSize)
          return focalLength
  
      # This will return the real world distance of the known object.
      def CalcualteDistance(self, perceivedSize):
          if self.focalLength == None:
              raise ValueError("Did you forget to calibrate this camera and set the perceived focal length?")
          distance = self.knownSize * self.focalLength / float(perceivedSize)
          return distance
  
subject: Update measured Focal Lengths for C920.