CU 4N5 - 9N
Under these standards it is the extremely complex to reach result above ~ 99,998 % (at correct calculation), at least, guaranteed or for one work cycle. Therefore, often for Cu 4N5-5N and above, the manufacturer establishes the specifications describing the own list of elements on which his purity is calculated and sometimes rules how to count up them to find this purity (whereas 100 % - the sum of described controllable impurities is correctly). In some tasks is admissible to not consider some elements, but these moments should be distinguished. For example, in cryogenic tasks any impurity have influence, some impurities have more influence, others less. Comments to Cu 5-9N are in section "Documents".
There are many offers of Cu 5N-9N on the market. Often they are not Cu 5N, and even not Cu 4N according ASTM B170 (USA). Cu 5N-9N measured under the reduced list of elements or with dodges of calculation can have characteristics worse than even 3N5-7 (M0б, C10200) according ASTM B170. Also some catalogues list copper as “Cu 99.9999% trace metals basis". The resistivity of such “Cu 99.9999%” is listed as 1.673 μΩ*cm at 20°C. In this case Electrical conductivity is only ~ 103.06% IACS. Copper ~99.995-8 % in accordance with GOST 859-2001 and ASTM B170 can possess such conductivity. Some sources assert that for very pure "correct copper of 99.999%", the electrical conductivity is not less than ~103.4-6% IACS and RRR >1000.