Quite right about the distinction between precision and accuracy. The classic science-and-engineering-course example illustrates the concept clearly:
However, high-end makers neither claim nor deliver better precision — or accuracy — than their more common counterparts.
Once you can produce a movement that's capable of a consistent rate of plus five seconds a day (precision), it's trivial to adjust/regulate it to stay dead-on (accuracy). Isochronism and rate stability — i.e. precision — is by far the more difficult part, and that's where a manufacturer like Rolex excels.
No high-end company claims to make better movements because of better timekeeping precision; that would be foolish. They're
finer and more costly simply because of the amount of skilled labour that they incorporate. A boring ol' machine-finished movement can be made with tighter and more consistent tolerances if the manufacturer is willing to invest in the production resources and quality control that it requires. With the delicate tasks of assembly, truing and adjustment done by hand in the case of Rolex, you get the best of both the mechanical and skilled-labour worlds as
timekeeping results are concerned.
The empirical results discussed in the "Inside COSC" article on TZ
support this, along with COSC director Jean-Pierre Curchod's assessment:
What about those expensive, lovingly handcrafted crafted, pursuit-of-perfection in-house movements? It is possible for such movements to reach chronometer standard, acknowledges Mr Curchod, but at the cost of much expensive and time-consuming tweaking. "It is more difficult and the failure rates are high — as
Since mechanical movements are inherently anachronistic, a certain level of imprecision is accepted. It's remarkable how good the results for the lovely horlogerie movements can be, all things considered. But don't expect them to deliver better timekeeping results than mass-produced ones; that's not what it's about.