The invention relates to a process for producing a diagram of an installation using apparatuses, each apparatus being supplied with gas, comprising:the consultation of one or more databases (5) comprising, for each apparatus, data on the flow rate, the nature, the purity of the gas supplying the apparatus, and the supply pressure of that gas for that apparatus,the selection, for each apparatus, of a value, or of a
limit value, of duration or of
frequency of use,the calculation, for each apparatus, of the consumption, or of the limit consumption, according to the utilisation value and to the flow rate data,the calculation, for each gas and for each gas purity, of the total of the consumptions of all of the apparatuses,the indication of technical constraints,the consultation of a
database (5) for proposing, for each gas and each gas purity, a packaging, as a function of the consumption and of the technical constraints relating to the storage of the gas and / or to their delivery.