I found the previous thread in which we waded through this confusing mess
http://doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=21420&page=82&fpart=1To quote Rocketman:
"Guns marked for 3 tons of service pressure (understood to mean that the proof load was 850 bar) and guns marked for 850 bar of proof pressure (understood to mean that the service pressure is 650 bar). We have two uses of pressure (service load and proof load), we have three measurement systems (lead crushers, copper crushers, and piezo), we have two standard systems of measure units (USA/English and SI) and two differing units (psi and tons and bar and Kg/Cm sq)within each system, differing proof laws by country, and differing proof laws by age."