THE CALCULATING RULE
If the pilot or commander of a boat is not familiar with the use of the standard air navigation computer, it will take some time and patience to master the calculation system. It is a circular slide rule, which allows multiplications and divisions for the calculation of times, distances, consumption
fuel, speed, etc., that is, all the problems that can arise during air navigation.
Examining the watch, we find an internal scale on the rotating bezel, which carries the digits of 10 to 10 (the digit 10 could be 1, 10, 100). In this instruction bulletin, we will call this disc: the movable disc. A second disc is located around the dial; we will call this disk: the hard disk. It should be noted that the movable disk digits will always relate to miles (or km.) Or miles per hour, feet (or meters) or feet per minute, gallons (or liters) or gallons per hour, or any quantity that varies with time. The hard drive digits will indicate minutes and hours in all time-related issues. On the hard disk, at 60 min., We find an arrow with the indication MPH. This sign represents the hourly speed reference, or the "hours" reference. This reference point is used in the solution of all problems concerning each quantity in relation to the hour (for miles as for km).
Clock / Instrument designed for pilots, sailors and divers