Every measurement
has a little room.
Read the scale. Explore the ±. Discover how careful measurements make stronger chemistry.
Look closely · Measure thoughtfully · Build confidenceHow much does the ± matter?
Shaded apparatus with a front-on scale for accurate reading.
A magnified view of the stated measurement interval. It is not a guarantee that the true value lies inside.
See where every number comes from.
For a concentration proportional to mass × pipette volume ÷ (flask volume × titre), this school-level method adds percentage contributions. It is an approximate additive bound. Edit each stated tolerance; the defaults are examples.
What do your repeats tell you?
Half-range describes the observed spread. It is not a confidence interval or a general formula for uncertainty of the mean. Identical repeats still have instrument uncertainty.
Put your measuring eyes to work.
A few things worth understanding
Uncertainty is not the same as error. Error is the difference from a reference value. Uncertainty expresses doubt associated with a measurement result. A discrepancy alone does not identify a particular mistake or prove a systematic error.
Our calculation convention: add absolute uncertainties for sums and differences; for products and quotients, add percentage uncertainties as a first-order bound. This school-level method is different from combining independent standard uncertainties in quadrature. Follow the convention in your question.
Readings and tolerances: half the smallest analogue division is a common classroom estimate. A manufacturer's stated tolerance takes priority. Display resolution alone does not determine the full uncertainty of a digital instrument. A delivered-volume tolerance for a pipette or flask should not automatically be doubled.
Precision and accuracy: close repeats indicate good repeatability. They do not prove accuracy or remove a common calibration offset. Half-range is a simple description of spread, not a substitute for a full uncertainty analysis.
Explore more: Titration Lab → · Chemistry practical handbook · NIST uncertainty guidance