Using the example of a project at 60 beats per minute, every beat is 1 second, or 1000 milliseconds. And since Beatcraft defaults to 4 steps per beat, that means each step is 250 milliseconds (or a quarter of a second long). That means the first 5 steps will occur at time:

0, 250, 500, 750

At 100% swing, every other step would be offset by exactly half the length of the step. So, if each step is 250 milliseconds long, and swing is 100%, every other step will be delayed by 50% of 250 milliseconds, or 125 milliseconds. So the timing would be:

0, 375, 500, 875

Likewise, at 50% swing, every other step would be offset by 25% of 250 milliseconds, or 62.5 milliseconds:

0, 312.50, 500, 812.5

This should be true for any step that's swung.. 100% = 50% of the step's length.