International comparisons of He-Ne lasers stabilized with /sup 127/I/sub 2/ at /spl lambda//spl ap/633 nm

After the adoption of the new "mise en pratique" of the definition of the metre in 1992, a wide programme of laser comparisons at /spl lambda//spl ap/633 nm, the most used of the recommended wavelengths, was carried out involving national laboratories and the BIPM. Twelve comparisons were made involving thirty-six laboratories, which, for this propose, worked in regional groups. Except for a few lasers which exhibited some malfunction, when the lasers being compared were adjusted to have the recommended parameter values, their frequency differences lay inside the standard uncertainty (2,5 parts in 10/sup 11/) given in "the mise en pratique".