A method for making on-line purchases includes purchasing a card having a unique identification code and a predetermined cash balance and activating an associated account. The invention also relates to a method for producing porous matrices, to matrices obtained according to said method and to a special method for obtaining cells for the inoculation of an implantable matrix. Two giant water basins are installed on top and under the building and the primary energy source is solar. The plant tray defines a tray cavity and a tray top opening communicating with the tray cavity. The secondary gas passage includes a main gas channel, an adjacent gas channel extending downstream from the main gas channel adjacently and substantially in parallel with the main gas channel, and branch gas channels branching off from the adjacent gas channel and continuing to the intake passages. The method includes an error correction procedure that increases measurement accuracy.