LB - The box is covering both bases; 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. I think it is remarkable that we get it as clear as we do!!
If you are going to shoot 100+ year old guns, you will have to get past looking for the simplicity of simple conversions and understand what the proof markings mean.
