Do you have a similar rating system like us? Here your dynamic rating changes after every match you play. Here a 5.0 is a 4 and 5.5 a 3, so let's say you're a 4.23 and beat a 3.85, you get a 2.85 and your rating improves, while your opponent gets a 5.23 and sees a decrease in his rating.
Yeah, in terms of league tennis at least. You start with a self-ascribed rating, and then you have what we call a dynamic rating, which takes your current match and averages it with the most recent three, so it goes up and down with every match as well. We also have year-end rankings that reflect your overall in the League Championship year.
For tournaments though, it doesn't really matter. You can enter whatever draw you think you can win.