| On the edge of the field, there are 2 'observing stations': a tripod with a board
onto which you tape a sheet of paper. There is a plumb line so that you can
align the edge of the sheet with vertical. On it, there is a PVC tube, which pivots on
a nail and is held with a cork.
When there is a launch, observers follow the bottle by looking through the PVC tube,
and leave the tube at the highest point. Draw a line along the tube and number it.
After 5 or so launches, remove the sheets and bring them to the board.
Then, on the board, I do the following (6) steps:
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