Does it all
Fill in the yellow boxes only Final comp O2 % EQUALISING Assuming one way valve from supply to base tank
base tank size litres   O2 added bar He % Here for Base tank of 10/50 supply tank size Litre
base tank pres bar   He added bar N2 % base tank size Litre supply tank pres Bar
base O2 perc % Top with O2 % bar base tank pres Bar supply O2 perc %
base He perc %   He % PPO2 @ PPo2 base O2 perc % supply He perc %
base N2 perc %   N2 % MOD m base He perc % Supply N2 perc %
Topped Presure bar MOD m base N2 perc %
  MOD m
  END @ MOD 1.3 m
END @ m