Our later instruments are built with internal adjusters, but the internal adjuster is a capricious and none too reliable mechanism. Its reliability depends largely on the assumption that such influences as time, temperature, vibration, shock, etc., which may tend to produce changes in the main optics, will nevertheless have no effect on the very similar but smaller adjuster optics; an assumption which is not invariably correct, since on occasion the internal adjuster will introduce more error than it will take out!
A Method of Calibrating Range Finders at Sea
By Commander Ralph C. Parker, U. S. Navy
The desirability of a method of correcting our range finders at sea, with the true range unknown, is too obvious to require comment. Much may have happened to them since we last could use some established calibration ranges in port; and after a prolonged cruise, radical changes in temperature, rough handling from the weather or possibly the enemy, our gunnery officer will approach battle or target practice hoping rather than knowing that his range-finder errors, as last observed, are still correct.