Sorry I missed your second question. I'm building what's called a "flowmeter", a device that measures flow speed. Depending on the application you need to do that in a specific manner. For instance this application requires high precision for very low flows, for which standard venturis are unfit, so a special method that relies con capillaries is used to get the poiseuille flow, which allows to get more precise and stable measurements for low flow ranges (below the speed at which we breathe).