An amazing nautical calculator

This is my reconstruction of an Italian speed-time log scale used onboard ships until the 60s.

Today it's impossible to get one, but in modern examination texts you can still found questions about its use, though nobody knows this simple tool anymore. The upgrade of the examination texts is sometimes very slow!

Speed-Time Scale

In this calculator only the numbers are given: "0.9", "9", "90", "900", "9,000" are always read as "9" and how to locate the dot or how to add tenths or hundreds we must find by ourselves, but it is always instinctive to know if we are dealing with tens, hundreds or thousands. For convenience, the examples are in kilometers, but can also be calculated in miles or nautic miles without any difference, just imput the value to get the right answer.

Instructions

Multiplication

Es. 32 x 5:

place the left end of a dividers on 1 and the right end on 3,2;
keeping the same opening, place now the left end on 5: the right end will indicate16. Take into account the position of the decimal point and add one zero to obtain 160, the correct answer.

Division

Es. 900/5:

place the right end of a dividers on 9 and the left end on 5;
keeping the same opening, place now the left end on 1: the right end will indicate 1,8. Take into account the position of the decimal point to obtain 180, the correct answer.

Time required

Obtain the time required for travel 140 kilometers driving at 120 km/ h:

place the right end of a dividers on 60 and the left end on 12;
keeping the same opening, place now the left end on1,4: the right end will indicate 7. Thus the time required is 70 minutes (1:10 hours).

Mileage

Obtain the mileage when the speed is 120 km/h and the running time is 1 hour and 10 minutes:

place the right end of a dividers on 60 and the left end on 12;
keeping the same opening, place now the left end on 7 (70 minutes): the right end will indicate 1,4. Thus the mileage is 140 kilometers. li

Average speed

Obtain the average speed (km/h) having traveled 140 kilometers in an hour and 10 minutes.

place the left end of a dividers on 1,4 and the right end on 7 (70 minutes);
keeping the same opening, place now the right end on 60: the left end will indicate 12. Thus the average speed is 120 kilometers per hour. li

Rate of fuel consumption

Obtain the rate of fuel consumption (liters/h) when the running time is 3 hours and the total fuel consumption was 60 liters.

place the right end of a dividers on 18 (180 minutes = 3 hours) and the left end on 6;
keeping the same opening, place now the right end on 60: the left end will indicate 20. Thus the fuel consumption rate is 20 liters per hour.

Fuel required

Obtain the fuel required for a trip when the rate of fuel consumption is 20 liters per hour and the estimated running time is 3 hours:

place the right end of a dividers on 60 and the left end on 20;
keeping the same opening, place now the right end on 18 (180 minutes = 3 hours): the left end will indicate 6. Thus the fuel required is 60 liters.

Estimated running time

Obtain the estimated running time when the rate of fuel consumption is 20 liters per hour and the tank has 60 liters of fuel:

place the right end of a dividers on 60 and the left end on 20;
keeping the same opening, place now the left end on 6 (60 liters): the right end will indicate 18. Thus the estimated running time is 3 hours (180 minutes = 3 hours).

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