Hi Orene, Thanks for the great question!

The markings on the tube actually correlate to cm of suction rather than Bars. The max pressure that can be applied is 7 cm of suction which corresponds to approximately 0.007 bars of suction. In order to setup the infiltrometer you begin by filling the top chamber 3/4 full of water. The water level will sit slightly below tube that runs from the top chamber to the bottom chamber. You then set the desired suction buy pushing the tube with the cm markings into the water at the marking which corresponds to the suction that you wish to apply. You can see an example of this in figure 4 of the Mini Disk Infiltrometer manual. I hope this helps answer your question.