The Navigation Computer - Distance, Speed, Time and Conversions — Page 103, Lesson 100

Let's finish the fuel conversion we started. We had the inner scale set for 250 imperial gallons, and we already did the litres conversion — 1135 litres. Now for pounds weight. Keep the inner scale exactly where it is. Move the cursor to 0.80 on the Sp.G lbs scale. That's the specific gravity scale for pounds. It's marked from 70 to 95, which represents specific gravities of 0.70 to 0.95. Read off 20.0 on the inner scale. Now check the order of magnitude. We're dealing with 250 imperial gallons, and the specific gravity is 0.8. So we expect roughly 2000 pounds. And indeed, the answer is exactly 2000 lb. Now the conversion to kilograms. Again, don't move the inner scale. Move the cursor to 0.80 on the Sp.G kgs scale. This scale is marked from 70 to 90, representing specific gravities of 0.70 to 0.90. Read off 9.08 on the inner scale. Check the order of magnitude. Either way you estimate — 1135 litres times 0.8 is about 900 kg, or 2000 lb is just under 1000 kilograms — the answer is 908 kg. So the key point: the same inner scale position, but you use different specific gravity scales depending on whether you want pounds or kilograms. The pounds scale goes 0.70 to 0.95, the kilograms scale goes 0.70 to 0.90. Now, the rest of this section is practice questions. There are three sets: distance, speed and time tabulations; fuel flow calculations; and unit conversions. These are the book's practice questions — let's try them one at a time.