Hydrogen
a) Hydrogen purity in % (volume/volume).
b) Relative humidity in % (30% is nominal).
DM water
a) PH of DM water (less than 6.5 is acidic and more than 7 is alkaline where oxygen is not forming). PH is also called IP (isotopic purity).
b) Conductivity.
c) Copper traces.
d) Dissolved oxygen (to trace corrosion and 1.2% is more).