More on Units
•Conversion of units: Conversion factor, e.g.
•      1 mi / 1,610 m = 1 mi / 1.61 km = 1 .
•      240 km = (240/1.61) mi = 149 mi etc.
•Checking calculations: In physical equations like   A = B +C   the quantities A, B, and C must have the same dimensions or units. For instance length in m or area in m^2.