This is used mainly be engineers. However, many people use it intuitively in real-life (non-engineering) situations, for example: to find the distance between two points on a road, with road distance markers "5 km." and "7 km.", you can subtract any of the numbers from the other, and get either 2 or -2. Since you are not interested in the direction, only in the distance, you then take the absolute value. Alternately, you can arrange the numbers so that you subtract the smaller number from the larger number from the start.
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