When you need to calculate an angle from a Vector2 structure, you can use this piece of code:

```
public static class Vector2Helper
{
public static float CalculateAngle(Vector2 v)
{
float angle = 0.0f;
if(v != Vector2.Zero)
{
v.Normalize();
angle = (float)Math.Acos(v.Y);
if(v.X < 0.0f)
angle = -angle;
}
return angle;
}
}
```

I used this to calculate an angle from the Vector2 of the Left Stick.

The original credit for this source code comes from here.