www.pilotballoon.com "the pilot balloon web resource"
Pilot Balloon - Meteorological Plotting Boards
Observations of a pilot balloon ascent, made by a theodolite are solved for wind speed and direction by graphical means using a plotting board. This method was used in the United States military and civilian weather services until the wide spread adoption of computer programs for solving the sightings. Boards like these were used with a standard slide rule as opposed to the U.K. Met. Office Pilot Balloon Slide Rule.
Below is a 1966 Navy pattern Meteorological Plotting Board (manufactured in 1982.) It measures 24" x 24". It has instructions for use imprinted on its surface and two wind speed scales. An almost identical model was produced at the same time as the one photographed labeled Meteorological Plotting Board U.S.N. 1981. Its construction utilizes plastic edges as opposed to the board below which has metal sides, it is a bit lighter but all other aspects of the board appear to be identical.
A board manufactured to a different specification was produced for the U. S. Weather Bureau. This board was called "Winds Aloft Plotting Board" measuring 35.5" x 35" it had 6 wind scales and did not include imprinted instructions for use.