A few astute students noticed that you may have a slight issue when you are finding your calculated velocity after you apply the differential pressure offset to your measurements. It is possible that you might get a negative measurement (obviously non-physical).

The issue boils down to the almost closed valve positions (low flow rates), because the differential pressure is so close to 0 with the high pressure line disconnected that you have to be much more accurate with your pressure reading. In reality, there is some variation in the offset with flow rate, but I only had all of you find one offset for all the data. If you think about it, even with the offset, the confidence you have in that measurement is probably fairly low because you are subtracting two relatively large numbers to try and arrive at a very small number (this means the uncertainty is significantly more than the average measurement!). I would note it in your report, and just not use these obviously non-physical values (which is a redundant measurement already), and state why you decided to remove them from the velocity calculation analysis.