Basic rules
Do
Specify the arc's starting point, full range and current value so progress is readable.
Provide a readable value and unit and calculate the target proportion on a consistent basis.
Associate each arc with a name and value and identify separate targets when applicable.
Don't
Do not compare arc lengths at different radii as if they encoded equal quantities.
Do not show an arc without a reference or silently lower a value to hide target overflow.
Do not imply better performance merely because an outer arc is longer.