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Let’s say you are preparing to go camping and mountain climbing. When you look through your supplies, you find ropes of many sizes. Two of them are tied in knots. You think that combined the two knotted ropes might be long enough for your plan, but you aren’t sure. So what do you do?

Easy: you untangle the ropes so you can measure them.

Adding decibels works the same way—they need to be untied before you can use them to go adding ...