Coincidence Rangefinder
Coincidence Rangefinders were instruments that offered the operator a monocular view of the object being ranged upon and required him to align two halve images to ascertain the estimated range. This type of rangefinder was used in many navies. Most notable amongst them were the variety of Barr and Stroud models the Royal Navy's ships employed for Fire Control.
Common Characteristics
The quality of the data obtained by visual rangefinding depends on the skill of the operator, the range to the object (short ranges are much more accurately measured), and often the size, nature and level of maintenance offered to the instrument employed. The atmospheric conditions, vibration of the platform and amount of available light also play a role in how accurately ranges would be measured.
In practice and particularly in action, the accuracy of rangefinders proved far less than the builders and users had hoped.
See Also
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