In science, a numeric value is meaningless unless it has a unit of measurement associated with it. For example, if asked how far is it to the next town and you answered "three", that answer would be meaningless. Did you mean 3 miles, 3 kilometers, 3 minute walk, 3 day horse ride? When performing calculations, it is advisable to keep the units in the calculation process. This will predict the meaning of the final numeric answer and help you trouble shoot errors in the calculation. For example, What is the speed of a bicycle that travels 100 meters in 25 seconds? speed = distance / time speed = 100m / 25s = 4 m/s The answer is stated in meters per second, which lets you know that you performed the calculation for speed correctly. What is the speed of a train that travels 900 m in 45 seconds? 40,500 m/s 0.05 m/s 20 m/s 20 m