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.