Why are some windshield wiper blades designed to be long and short?

Many people install windshield wiper blades do not know a long short two wiper's left and right position, often mistaken, then why the car windshield wiper blades are not the same length?

A piece of glass, as shown in the picture below, theoretically, windshield wiper blades scraping as long as can meet the requirements of the regulation of coverage in the area a (main driver) coverage of more than 98%, B area (deputy driver) covers more than 80%.

Today, most of the car windshield wiper blades work is from left to right in the same direction brush, that is, shun scraping.

As shown in the following illustration:

Obviously, in order to not and the right (main driving position) scraping in the middle of the process of scraping "fight", the left side (copilot) of the general will be slightly shorter. So, generally see the car windshield wiper blades a long and a short time, is basically the case.

So even if it's a scratch, is it possible to have a scratch on the left side (the driver's side) that is longer or as long as the scraping piece on the right (the main driver's position)?

Theoretically, it is possible to meet the requirements of coverage. But look accustomed to the main drive windshield wiper blades length is larger than the co-pilot, rarely will appear above. At the same time, in the car assembly line, many workers are also accustomed to the long windshield wiper blades mounted on the main drive side (right), the short windshield wiper blades installed in the side (left).

Therefore, in order to increase the driver's vision in the rainy day and avoid the two windshield wiper blades scraping when the collision, out of habit we are generally the long size windshield wiper blades installed in the main driving position, the short size windshield wiper blades installed in the co-pilot.