Indeed as I wrote above APT is one of the inspirations for this.
I'd be curious for suggestions how we can be better than APT. E.g. the two circles that indicate the Focus error in APT.. are they really useful? Why use circles here? What is measured is just a single number.
Instead what I want to provide is an uncertainty of the measurement, so that the user sees when they have reached the sensitivity of the method and further tuning becomes pointless.
This can be expressed visually through a "Focus achieved" message.

BTW: is color vision deficiency (CVD) a design consideration in KStars? Might be an issue when we use differently colored indicators.

Cheers, Sebastian