"Further examples of such measuring systems known per se to those skilled in the art, especially systems made up of compact, in-line measuring devices, are explained in detail in EP-A 984 248, GB-A 21 42 725, U.S. Pat. No. 4,308,754, U.S. Pat. No. 4,420,983, U.S. Pat. No. 4,468,971, U.S. Pat. No. 4,524,610, U.S. Pat. No. 4,716,770, U.S. Pat. No. 4,768,384, U.S. Pat. No. 5,052,229, U.S. Pat. No. 5,0" . . . .