The tool calculates just how long you need for a trip. Of course you can also use a calculator or even mental calculation. It's faster with this helper. In practice the wind can change and so can the course. With this tool you can quickly determine in between how long you still need. Since you often have to cross and can not choose the direct way, the extended way is to be indicated as a percentage deviation. So you can even consider the detour in the time calculation.