Six minute rule
Six minute rule : a ruleofthumb shortcut, used in navigation, for easily determining the distance that a vehicle will travel
Navigation usually requires complex math, and navigators have long relied on aids like electronic calculators, mathematical tables, and slide rules. These devices take time and attention. Rules of thumb help busy sailors, aviators, and rally drivers make decisions without needing to pick up a tool.
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To calculate the distance that a vehicle will travel, a navigator can use the sixminute rule.

Let’s say that a ship – a fast ship – is traveling at 18 mph. ^{1} The ship’s navigator wants to know how far the ship will go in six minutes.

We know that in an hour, the ship will have covered 18 miles.

Six minutes is onetenth of an hour. In six minutes, the ship will travel onetenth of 18 miles. The navigator can shift the decimal point over. (No calculation required!) In six minutes, the ship will travel 1.8 miles.
Our navigator can extend the sixminute distance to calculate mileage in other intervals. In 12 minutes, the ship will cover twice the sixminute distance: 3.6 miles.
This will also work for a car on the highway. At 55 mph, a car will cover 5.5 miles in six minutes. Ten miles will take a little less than twelve minutes.

For maritime use, the units should probably be knots and nautical miles, but we use miles for clarity. Similarly, we’ll discount the effects of winds or current. ↩