Here is how to create a chrome-look volume knob and an indicator that goes from green to red. This uses gradients along the stroke of the line to create these cool effects. And, of course, it is super easy to do!
Create a circle that is half the size of the volume knob you want.
Apply a stroke the the line large enough that it looks like the circle is filled. The stroke will make the circle twice the size as the stroke is added to the inside ad outside the circle equally.
In the Gradient panel, select the stroke icon, select the Apply Gradient Along Stroke selection (this is key to making it work)and choose a black and white gradient.
Once the stroke gradient is applied, this is the result.
On the gradient ramp, add color stops (by clicking below the ramp). Alternate the colors from white to 70% gray (double-click on the color stop to change the color), making sure you end up with the same color at the start and at the end for a smooth blend. Space out the color stops evenly along the ramp.
This is the result of the multi-stop gradient along the stroke.
Add a circle for the indicator on the dial. Apply a gradient fill to this.
Choose Object > Path > Offset Path and set the off set to -3 and click OK. This will create a smaller circle on top of the larger circle.
Rotate the new circle 180° to make is look dimensional.
Create a circle outside the knob. Add a stroke and no fill.
In the Stroke panel, set the Cap end to rounded (hot dog the ends), check the Dashed Line box and set the dash to 0 and the gap to 30. The higher the number for the gap, the less dots will appear on the line.
Rotate the dotted circle 45°. Adjust the stroke weight of the line to get the dots to look the right size.
Use the Direct Selection tool to select and remove the lower section of the circle.
In the Gradient panel, apply a gradient to the stroke and set the stroke option to Apply Gradient Along Stroke. Create a gradient with a green color stop at the start, a yellow color stop in the middle and a red color stop at the end.
This is the result of the gradient along the dotted stroke.
Apply an Outer Glow (Effect > Stylize > Outer Glow) to the dotted line.
To make the glow stand out, draw a rectangle, fill it with 90% black and move it behind the knob.
To create a slip shadow coming off the knob, create a rectangle that width of the knob.
Rotate the rectangle 45° and set the opacity at 20%.
Apply and Out Glow to the knob to create a bit of dimension.