Minor correction needed!
The K-14 sight was not adjusted for target type. Instead, the sight controls were set for the wingspan of the target.
The diameter of the circle of diamonds was controlled by a rotating sleeve on the throttle. By "twisting" this, the pilot could make the diamond circle diameter increase or decrease.
Once behind the target, the pilot twisted the throttle to superimpose the diamond circle diameter over the wingtips of the target. This adjustment setting was used by the sight ballistics computer to compute range. This process is known as "stadiametric ranging" and involves the comparison of a known reticle diameter to a known target size. The result is range.
Stadiametric ranging is based on the idea that an angle of arc will span a certain amount of feet at a given range. Gunsight reticle diameters are made to be a specific size...the unit of "size" is called "mils" which is a unit of angular measurement (there are about 18 mils in one degree).
The basic idea is that one mil will equal one foot at 1000 feet range. If a gunsight reticle diameter is 35 mils wide, then a target with a wingspan of 35 feet will just fit inside the reticle at a range of 1000 feet.
In the K-14 gunsight, the reticle diameter size was sent to the computer by the throttle twist setting. The pilot had already told the computer what size target he is after. So the computer takes this wingspan value and compares it to the throttle input and computes range. For example, the target size is set at 35 feet. The pilot twists the throttle to match the reticle to the target wingspan. The computer then reads this value. Let's say the pilot had increased the size of the reticle to 70 mils. The computer would say, "target span = 35', reticle setting = 70 mils, therefore target range = 500'". This range value was used to calculate a bullet time of flight that was used in the overall lead angle calculation.
Besides range, the other major variable in the lead angle problem is target crossing angle. The pilot solved for this variable by keeping the sight pipper (center dot) on the target. He had to "track" with the pipper on the target for a minimum of one second before firing. This one second was known as "sight settling time" and was the time needed for the sight computer to reach a valid solution.
Pilots were taught a technique known as "track - shoot - track". This was intended to place emphasis on the need to keep the pipper steady on the target to allow the sight to compute lead accurately.
We still teach the same technique today.
Andy
