Page from Stockhausen's Studie II
'The generation of rhythmic material was only one side of the problem: its notation also proved a challenge. The more complex it became, the less exact the result in actual performance, so that Stockhausen was able to describe notation as dependent on "uncertainty factors" occuring within fields whose size was relative to the complexity.' 2626. This, as Ligeti noted, had been a problem since the early twentieth century: see dRV (D), 38-40.
Source: Serial Music, Serial Aesthetics pg139 (M.J. Grant).