Beginner Java Help - Question 1

[alexander.h]

Hello! I'm new to Java (we're planning to switch to it next year after passing the last three years using Labview) and I have one important question. In the "Getting Started with Java for FRC" pdf, it shows the following code for an autonomous that drives in a square pattern by driving half speed for 2 seconds, then turns 90 degrees. This is repeated 4 times :

public void autonomous() { 

     for (int i = 0; i < 4; i++) { 
          drive.drive(0.5, 0.0); // drive 50% fwd 0% turn 
          Timer.delay(2.0); // wait 2 seconds 
          drive.drive(0.0, 0.75); // drive 0% fwd, 75% turn 
       } 

     drive.drive(0.0, 0.0); // drive 0% forward, 0% turn 
}

What I don't understand is why it's a 75% turn for a 90 deg turn? Is there some way this was calculated?

Thanks!

P.S. I called this "Question 1" because I know that I will have other questions about Java in the future!