Dreyer Calculator
The Dreyer Calculator was a British Fire Control Instrument that determined the aggregate effect on gun range attributable to a number of factors. It was invented by John Tuthill Dreyer, brother to Captain Frederic Charles Dreyer and worked in concert with his brother's fire control table.
Visible are the means of setting the Air Density, Range Rate, Plot Range, and Wind along the line of fire. The range spotting correction is read off of scale H. Only the grayish piece N is peculiar to the gun system in use.
The Dreyer calculator was a small calculating board that eventually enjoyed a place on the bulkhead of Royal Navy Transmitting Stations. It calculated several separate factors that would cause the Plot Range and Gun Range to differ and summed them together to produce an aggregate spotting correction for range.
In ships with Dreyer Fire Control Tables, this correction would be entered into the Spotting Corrector as a Straddle Correction.
Inputs and Mechanical Design
The Dreyer Calculator was customized to a given Gun System by the choice of which backplate (bearing the range scale) was fitted. Milled curves along these backplates expressed ballistic relationships taken from the Range Table, such as range to time-of-flight.
The inputs were:
- Range Rate
- Air Density (difference from the standard atmosphere of the range table)
- Wind along the line of fire
- Plot Range
By entering the plot range, the backplate's milled curves would expressed a time-of-flight, and this was the means by which the other 3 inputs could weight their effect on how the range would alter during time-of-flight.
See Also
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