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Accuracy and PrecisionAccuracy and Precision
Difference between Difference between accuracy and precisionaccuracy and precision
Accuracy- how close you are to the Accuracy- how close you are to the actual answeractual answer
Precision- how close all of your Precision- how close all of your answers are to each other answers are to each other
Accuracy is a measure of your lab Accuracy is a measure of your lab technique, precision is a measure technique, precision is a measure of your ability to duplicate what of your ability to duplicate what you just didyou just did
Dart Board Metaphor Dart Board Metaphor high accuracy low precision high precision low accuracy
low accuracy and precision high accuracy and precision
Measuring accuratelyMeasuring accurately always report all numbers given on always report all numbers given on
a digital readout (Do NOT round)a digital readout (Do NOT round) Do NOT add or delete zeros from Do NOT add or delete zeros from
the end!the end! Make sure your reading is stable!Make sure your reading is stable! Always read your equipment as Always read your equipment as
accurately as you can (take your accurately as you can (take your time, get close to the instrument.time, get close to the instrument.
Using a Graduated Using a Graduated Cylinder.Cylinder.
Pour the liquid in a graduated cylinder and read from the meniscus.
water
air
meniscus ALWAYS PUT YOUR HEAD AT THE SAME LEVEL AS THE MENISCUS
The water will “grip” to the edges and form a depression in the middle, the lowest point of this curve is the meniscus.
Reading between the linesReading between the lines
Estimate one place on non digital Estimate one place on non digital equipment. (rulers, graduated equipment. (rulers, graduated cylinders)cylinders)
6 7 cm6.42 cm
If it is exactly on the line
6.60 cm
Reading between the linesReading between the lines
Estimate one place on non digital Estimate one place on non digital equipment. (rulers, graduated equipment. (rulers, graduated cylinders)cylinders)
6 7 cm6.25 cm
If it is exactly on the line
6.90 cm
Reading between the linesReading between the lines
20 30 cm
Graduated CylinderGraduated Cylinder
20 mL
10 mL
17.2 mL
What’s the differenceWhat’s the difference
between 6.6 cm and 6.60 cmbetween 6.6 cm and 6.60 cm The difference is how accurately The difference is how accurately
you were able to measure.you were able to measure. More accuracy is always better but More accuracy is always better but
you can NEVER be exactyou can NEVER be exact You must report how accurate you You must report how accurate you
were.were.
Measuring preciselyMeasuring precisely
If possible always measure three If possible always measure three timestimes
If one measurement isn’t close to If one measurement isn’t close to the others always measure again.the others always measure again.
It is always a good idea to have It is always a good idea to have your lab partner take the same your lab partner take the same reading as you to make sure you reading as you to make sure you are reading it correctly.are reading it correctly.
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