Hi Alex,
In the default setting the loop is created per second. If you slow down the loop by four, the whole loop will be given in 120 frames.
A good loop excludes the last frame, as it would be the same a the first, which might be noticeable as a short stop. Like 0º is suppose to be equal to 360º
The “Sin” is just to smooth the animation, as it loops through the 360º one time through, with a nice soft curve, a sine curve, like an S horizontally.
The t in the formula is connected to a slider. While the Formula Effector is selected>Attribute Manager>Effector: swirl open the Variables. Set the t slider to any value you like, the slider is only limited to -100% to 100&, but the fields can take larger/smaller values. So, to slow it down, the t should be at 0.25 four your value 4. (1/4)
I hope that helps. If you have a specific scene file, I’m happy to look into it.
All the best