What is the difference between Accuracy and Precision?

Accuracy & Precision: The story of the cross-bow and the apple

We recently watched a fascinating TED Ed talk by Matt Anticole on YouTube about the difference between accuracy and precision.  Matt uses an analogy of the legend of William Tell, the Swiss folk hero.  

William Tell was an expert marksman with a crossbow who was arrested with his son when he refused to be respectful to the King.  The King said that both he and his son would be executed, but then he King told William Tell he could save his son’s life if he shot through an apple placed on top of his son’s head.  In the legend William Tell is able to shoot the apple and save his son’s life.

The talk considers two alternative scenarios.  Firstly, what would have happened if William had his crossbow stolen and replaced with an inferior version.  In this case, the inferior tool (crossbow) could have impacted accuracy and risked hitting his son rather than the apple.  The second scenario talked about William losing confidence in himself, leading to him having a nervous shaky hand. This would affect precision.  

Matt goes on to explain that accuracy involves how close you come to the correct result. To use the bow and arrow analogy, if William Tell were target shooting, his accuracy is how close his arrows come to the target’s centre or “bullseye”. For digital scales, it is important to know your scale’s calibration and use good measuring technique to hit your mark accurately. In our recent blog post we talked about making accurate weight measurements with scales. Measurement accuracy is of high importance for scientific research. Measurements taken during experiment usually have their accuracy or “uncertainty” listed. This uncertainty value takes into account specifications of the scale and information on its calibration such as the accuracy class of the calibration weights last used to calibrate.

Precision is how consistently you can get the same result.  In the bow and arrow analogy, precision would be how often you hit the same spot on the target each time, even if it’s not bullseye. If William Tell were using a stolen bow with unknown calibration, he might shoot his arrows along the same path each time, but without knowing that particular bow, those shots might be off the mark. He would have high precision, but low accuracy. Some tasks do not require accuracy so much as they do precision. For instance, if you are trying to use a scale to split something into equal parts, you do not need to know the accuracy of the weight values so long as it is precise and gives repeatable results. Precision may also sometimes refer to scales with very high sensitivity and therefore small display increments. Our MTT-100 high precision scale features an incredible 0.005g readability.

Another field where accuracy and precision are essential is when weighing out ammo for reloading.  Using the correct tool for the job will always make the process smoother and safer. We have scales built specifically for reloading to ensure an accurate AND precise result every time.  The SHARPSHOOTER is our ultimate reloading scale. The high precision sensor provides 0.05 grain (0.001 g) readability for superior results. 

If accuracy and precision is important in your field of work or hobby, then we highly recommend watching the TED Ed talk, its very clear with some great visual animation too.  If you are reading this and you haven’t tried a Truweigh scale before, then be sure to look out for our products at your local supplier.  We are rapidly expanding our distribution partners here in the US so that you can find accurate & precise digital scales in your state or city.  For wholesale options, please get in touch.