Author wrongly presumes that people using the metric system are not visualizing the measures in almost the same way. We do. One step is about a meter, or the width of finger is about 1 cm. More often used 10 centimeters (1 decimeter) is approx. a distance from your thumb to the index finger. It's all about being used to certain system of measures, so that you can automatically relate the measure to something from the real life for comparison, e.g. my car is 5m long, also the wall in my room is around 5m, so if you ask me how big is 5m I can instantly visualize the distance very accurately (without even consciously thinking about cars or walls)