What does the 1-6 speed setting on the TS 55R EBQ saw mean?

The TS 55R EBQ saw is rated 2000-5200 no load speed and is broken down into 6 speed settings:
1 = 2000rpm
2 = 2640rpm
3 = 3280rpm
4 = 3920rpm
5 = 4560rpm
6 = 5200rpm

Blade speed is adjustable for cutting materials with most appropriate blade and getting the best quality of cut.