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Homework Help: Sig Figs query for a steady flow pipe

  1. Nov 30, 2013 #1
    1. The problem statement, all variables and given/known data

    First let me say i'm new to lab reports at Uni, and i'm dreadful at them...

    I'm having issues with how many sig figs to correctly display on a data table for an experiment i've done to investigate the Reynolds number. One particular step is to find Δp at different stages on a manometer using the equation Δp=(ρwater-ρatm)gΔ(Zw) with Zw being the difference between the left and right hand side of the manometer. all my Zw values are in mm; for example one of them is 33mm, using the equation for that particular value I get 323 Pa, I've looked around and it seems that the value I should display on the table is 320 Pa as the value I obtained should have the same SF as the lowest SF of the value used to calculate it. This seems ok for lower values but looks wrong at higher values because it feels like I'm rounding up and down a lot of the value. I would be thankful if someone could tell me if I'm going wrong and the correct procedure when dealing with SFs from measurements taken in experiments.

    2. Relevant equations


    3. The attempt at a solution

  2. jcsd
  3. Nov 30, 2013 #2


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    Staff: Mentor

    What do you mean with higher values?
    Rounding to two significant figures is fine for a final result. It is not a proper treatment of uncertainties anyway...
  4. Dec 1, 2013 #3


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    Staff: Mentor

    Don't mistake reported values for those used in calculations. Your report should contain rounded numbers, but you should never used these rounded values in your calculations. Use either full precision as spit out by your calculator, or at least use so called guard digits - that is, use several digits more than you are reporting.
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