View source for Dreyer Calculator

The '''Dreyer Calculator''' was a British [[Fire Control Instrument]] that determined the aggregate effect on [[Gun Range|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 [[Dreyer Fire Control Table|fire control table]].
[[File:ProposedDreyerCalculator.jpg|thumb|512px|'''The Dreyer Calculator as Proposed'''<br>Visible are the means of setting the [[Air Density]], [[Range Rate]], [[Plot Range]], and Wind along the line of fire.  The [[Range Spotting Correction|range spotting correction]] is read off of scale H. Only the grayish piece N is peculiar to the [[Gun System|gun system]] in use, containing a "Wind Curve" (label obscured in this image by compositing) at the top, which affects the impact of Air Density and Wind on the output and a "Time of Flight Curve" at the bottom which affects the Range Rate's contribution. ]]

The Dreyer calculator was a small calculating board that eventually enjoyed a place on the bulkhead of Royal Navy [[Transmitting Station]]s.  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.

==Inputs and Mechanical Design==

A wooden case with a carry handle was envisioned, and the full size drawing seems to hint at dimensions of 33cm by 55cm with a depth of 65cm or so.

The 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|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 altering the plot range with a large knob, the backplate's "time-of-flight vs range curve" would interact with the range rate and a "wind vs range curve" would influence the degree to which air density and wind along affected the output.

==Application and Use==

In ships with [[Dreyer Fire Control Table]]s, this correction would be entered into the [[Spotting Corrector]] as a [[Straddle Correction]]<ref>''Handbook for Capt. FC Dreyer's Fire Control Tables'', p. ??</ref>.  

As the battle progressed, it was of course common for all the inputs (except air density) to change.  It would be a fairly manual task for someone to keep the Dreyer calculator updated and to feed the changing result back to the Dreyer table's spotting corrector.  I can imagine that ships lacking a tool similar to the spotting corrector would forego use of a Dreyer calculator and simply rely on spotting to account for these dynamics.

==See Also==
*[[Wind Dumaresq]]
*[[Ballistics]]
*[[Range Table]]
*[[Transmitting Station]]
*[[Dreyer Fire Control Table]]

==Footnotes==
<small>
<references/>
</small>

==Bibliography==
<small>
*{{BibDreyerTableHandbook1918}}
</small>

[[Category:Fire Control]]
[[Category:Shipboard Equipment]]