07-12-2020, 09:21 PM
As others have stated, accuracy is a measure of how much the measurement deviates from the known true value. The closer the measurement is to the true value, the more accurate it is. Normally, we measure things in triplicate or more, so we take the average of those measurements. One measurement by itself doesn’t really tell you much, other than how close ONE measurement is to the true value. It’s total accuracy can still be way off, because if I measure it again and it’s way off I then have no way of knowing which one is closer to the truth. Thus, more measurements leads to a better estimation of how accurate any measurement may be.
You really cannot use precision as a term with only one measurement, as precision is a measurement of how closely the previous measurements (plural) agree with one another. It has nothing to do with the true value and strictly speaking you cannot use the two terms (accuracy and precision) interchangeably. Analytically speaking, a balance is understood to have a precision of +/- the last digit: a balance measuring one decimal point is +/- one decimal point; one that measures to four decimal points is still +/- that last decimal point, unless otherwise stated. A balance that measures four decimal points (0.0000) inherently will give a mass reading that will be better known than one that only gives three (or fewer) decimal points, and this is often advertised as a more “precise” balance. Precise used in this manner really muddies the waters, as it doesn’t really describe precision. You may know the value more precisely, but it doesn’t imply more precision.
Any balance can give measurements that are wildly off, irrespective of its stated precision. Thus, analytical balances are calibrated against a known standard prior to use. Such balances are sensitive and will drift due to atmospheric conditions and thus must be calibrated. Things you purchase for personal use are calibrated prior to shipment, and are quite often robust enough to not be affected by a lot. Additionally they are made from materials that are often unaffected normal conditions.
Diana
You really cannot use precision as a term with only one measurement, as precision is a measurement of how closely the previous measurements (plural) agree with one another. It has nothing to do with the true value and strictly speaking you cannot use the two terms (accuracy and precision) interchangeably. Analytically speaking, a balance is understood to have a precision of +/- the last digit: a balance measuring one decimal point is +/- one decimal point; one that measures to four decimal points is still +/- that last decimal point, unless otherwise stated. A balance that measures four decimal points (0.0000) inherently will give a mass reading that will be better known than one that only gives three (or fewer) decimal points, and this is often advertised as a more “precise” balance. Precise used in this manner really muddies the waters, as it doesn’t really describe precision. You may know the value more precisely, but it doesn’t imply more precision.
Any balance can give measurements that are wildly off, irrespective of its stated precision. Thus, analytical balances are calibrated against a known standard prior to use. Such balances are sensitive and will drift due to atmospheric conditions and thus must be calibrated. Things you purchase for personal use are calibrated prior to shipment, and are quite often robust enough to not be affected by a lot. Additionally they are made from materials that are often unaffected normal conditions.
Diana