Beam Detector
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A beam detector is a collection of lines that are arranged in a circle such
that any line passing through the circle must intersect the beam
detector. For instance, a very simple beam detector would be a square that
completely enclosed the circle. One interesting question surrounding beam
detectors is: What is the shortest total length of lines required to
construct a beam detector? 

This model is of a beam detector that comprises a Steiner tree, a very
effective method of constructing a small beam detector. The model allows the
significant points of the detector to be moved and the other points (which
are fixed by the geometric construction) move accordingly. There is a blue
beam line which can be moved around the circle to show that it will always
intersect at least one line of the beam detector. The relevant values are
automatically kept up to date by dependency in the spreadsheet that is
displayed alongside the graphical depiction of the beam detector. 
