Ready Reckoner?

[Dominion]

Could anyone tell me more about the image I attached below? I've tried to research it online but come up with absolutely nothing besides it possibly being called a "Ready reckoner"? Are these particularly uncommon?

 

Thanks in advance!

[WhiteStarLine]

This has been playing on my mind this afternoon and my guess was it sat on a plotting table or similar for spotting and correcting artillery fire.  Royal Garrison Artillery fired large calibre rounds in howitzers and the angle between the point of impact and the target could be sighted and therefore adjusted if the object in your image was lightly screwed on a plane table (three screw marks in centre) with the angle of the target viewed along the Line of Fire.  The correction to the gun crew could be given in degrees if the observer knew how far away the target was (between 8,000 and 16,000 yards away).  It supports both degrees and the clock ray method.

 

J.H. Steward made astronomical, navigational and other precision instruments and there is a similar one to yours in the UK Science Museum.  They call it a ready reckoner but to me it seems more to lie in the plotting table or fire adjustment category.

 

Disclaimer - I was never more than a humble grunt, so hopefully a knowledgeable arty type will correct this post.

 

Image: Auto Range Corrector, artillery calculating device. Made: London. manufacturer: J H Steward

 

[Gunner Bailey]

I think it's a Fire Corrector calculator.

 

Similar in design to a pilot's navigation tool it allows the wind speed and direction to be taken into account before firing. More about left and right delfection than range I think.

 

My grandfather who was in the RFA 18pdr batteries would have recognised it though.

Edited 22 April , 2019 by Gunner Bailey

[Chasemuseum]

Its part of a plotting calculator for indirect fire. The dial is to assist in correcting the forward observer's corrections as his bearing to the target is different to the battery's bearing to the target (unless he is directly under the flight path of the shell). The fan is used with the observer's corrections of the observed shot, to move point of impact left or right, and to add or drop range. These all have to be converted to changes at the battery, with changes to the bearing of the dial sight and the clinometer on the guns. 

Cheers

Ross

 

PS  Gunner Bailey - your grandfather would most definitely recognised this and probably have known when this design came into use and been able to say when to use this one and when to use the other types. It's a very great pity we cannot ask him.

Edited 22 April , 2019 by Chasemuseum
added post script

[Dominion]

Thanks for the input, very much appreciated! Certainly an interesting piece of equipment