To follow on with what Sebastian has said, there is no "one, true" temperature for dark chocolate, one for milk chocolate, and one or white chocolate. Every chocolate will have its own set of working temperatures ... but those may change depending on the ambient temperature and humidity and the method of tempering being used. In large industrial processing situations they can control these variables very closely, but in the average small chocolate kitchen it's a different story.
In my experience, there is no substitute for being able to hand temper and to know what tempered chocolate looks like and how it behaves. You use that experience to help you arrive at the temperatures that work for you.
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
clay - http://www.thechocolatelife.com/clay/