Until calculus was invented, the only way to work this out was to cut the time into smaller and smaller pieces, so the average speed over the smaller time would get closer and closer to the actual speed at exactly 1.5 seconds. This was a very long and hard process, and had to be done each time people wanted to work something out. Certainly it is much more difficult for a driver to figure out a car's speed by using only its odometer (distance meter) and clock—without a speedometer.