1. This rule was used by the British Meteorological Office for calculating the course followed by meteorological ballons. It was used in conjunction with one or theodolites. Meteorological balloons, which were free floating despite the word "pilot", were used to obtain such information as upper air wind speed and direction.

2. This model was of the earliest type. They were manufactured from 1915 until the 1920s.

3. Most of what I know about this type of balloon comes the following web site:
   http://www.csulb.edu/~mbrenner/slide.htm

Detail - cursor and fixing nut