Conversion of units
A conversion factor is a ratio that lets one convert a measured quantity to a different unit of measure without changing the amount. When a conversion factor is multiplied by the item one are converting, it cancels out the units they does not want and leaves those that they do. Because the top and bottom of conversion factors are the same, conversion factors always equal 1. For example, a  conversion factor of (1 day)/(24 hours) equals 1, because 1 day = 24 hours.