Slide 2.1 Circles:
I am not sure if that is intended, but I would take a look at settings of your dial here (select the dial and open the design-tab in the menu). Your dial is set to start at 0 and end at 5 - that means there are 6 steps, but as far as I can tell you only have 4 layers to show. So you could change the dial to start at a value of 1 and end at 4. You could also change it to 360 degrees if you want.
Slide 1.1 and Slide 3.1
Similar thing here. Your dial is set to start at 0 and end a 3 (that makes 4 steps), but you have only 3 layers to show. So dialing it back to the start position (0) does not do anything that might confuse users. You could either add a trigger that hides all layers when the value of your dial is 0. Or you could change your dial to start at 1 and show the first layer right of the start by edding a trigger (that shows the layer when the timeline of the slide starts).
Slide 4.1
As for your windmill slide.
I find that sort of animation hard to do within Storyline.
I would try another approach here: If you have some expierence with any animation software: Build an animation of one rotation for each speed and export looping GIFs of those.
So you will end up with something like this:
- value = 0 => still-frame of the wings
- value = 1 => animated gif slowest speed
...
- value = 4 => animated gif highest speed
Import the still frame to Storyline add 3 more states to that still and put the GIF animations into that state. Than change the state with the dial.
You would have a still (no movement), when the dial is at 0, slow looping movement when it is at 1, and so on.