A product comprising an absorbent paper material and a dispenser adapted to hanging from a support such as a towel bar or a hook is disclosed. Once positioned, the output of the actuator may be locked by a locking mechanism to prevent this output from rotating to its quiescent position. The delivery devices are particularly adapted for use in minimally invasive surgical procedures. The creation request is processed to create a sparse database. Next, the carrier solution is slowly flowed at a predetermined speed, so that the gas exchange is fully conducted in the gas exchanger 7, the output potential difference V between the reference pH electrode 14 and the measuring pH electrode 16 at time t is found, and the difference V between the V measured at this time and the Vobtained at the last time, is obtained.