The ruler is used to empirically estimate on the paper map at a given scale, the distance, the flight time, and the windless consumption for each navigation leg for a given cruising speed and a given cruising consumption.
It should be considered as a quick and easy backup solution in the event of navigation equipment failure, in a process of redundancy of resources in addition to the devices usually on-board, and for which it can in no way replace.
Its use is carried out under the full responsibility of the user.
You can also estimate the flight time and the consumption with wind using 2 methods, one adapted to the flight and the other to the preparation of the flight.
In flight
Read the time “H1” at the starting point “D” of your navigation leg and choose an intermediate point “P” on it.
Using the ruler, read the estimated windless flight time “T” between the start “D” of the leg and the chosen point “P”.
When you reach point “P”, read the time “H2” to deduce the flight time achieved “T2” and compare it to the flight time without wind “T”.
This allows you to estimate the weather with wind over the entire section. You can also read the ruler as a correspondence table to deduce the consumption.
For example by taking an intermediate point “P” to a tenth of the leg, you have to multiply by 10 the difference between “T2” and “T” that you add to the total time of the leg provided on the ruler “T3”.
(T2 - T) x 10 + T3 = Time with wind for total navigation leg
In preparation for the flight
Although the ruler is not made for flight preparation, it remains possible to use it for this purpose to approximate flight time and consumption.
On the map, draw a line representing the navigation leg, the route “R”, from the starting point “D” to the ending point “A”.
Read on the ruler the windless flight time “T” of the leg, between “D” and “A”.
At the point of arrival “A” draw a line “V” in the direction of the wind (use the rosettes on the map).
The ruler shows wind measurements, from 5 to 25 kt, for specific time.
Place the ruler on the “V” point at the start of point “A”, and using the ruler's wind measurements mark point “X” showing the time “T” read previously (for out of range values add up the measurements, eg for 25min of flight, choose the 10min measurement + the 15min measurement of the ruler).
Connect a heading line “C” point “D” to point “X”, you get a speed triangle. Place the ruler on the “C” line to estimate your flight time and fuel consumption.
To go further, if you want to refine this approximation, you must consider the flight time “T” from “D” to “A” with wind.
In this case, extend your line “R” and draw a line “?” at a right angle to “R” and joining “X”.
Measure “?” and report this measurement to “R” materialized by point “O” located before point “A” if the wind is tailwind, and after “A” if the wind is head-on.
Draw the parallel “//” to “V” through “O”. Extend the “C” line so that it intersects “//” at “O”.
Place the ruler on the “C” line between “D” to “O” to refine your calculation of flight time and fuel consumption.