Precision and accuracy
Precision and accuracy in measurement are different, and often confused.
![](https://substackcdn.com/image/fetch/w_1456,c_limit,f_auto,q_auto:good,fl_progressive:steep/https%3A%2F%2Fbucketeer-e05bbc84-baa3-437e-9518-adb32be77984.s3.amazonaws.com%2Fpublic%2Fimages%2F96f7f12a-96d0-47ba-a2d5-2ad634071d10_320x214.png)
From here
Let's assume that we are trying to measure a property that has a value that is stable and that can be measured.
To measure a property we need both an instrument and a procedure. Using the same procedure with a different instrument or the same instrument with a different procedure will usually give a different result.
We'll call the combination of instrument and procedure a technique.
A technique for measuring a property yields accurate results if repeating the technique gives a series of measurements that, on average, converge on the "true value" of the property. This assumes that there is a knowable "true value."
A technique for measuring a property yields precise results if it repeating the technique gives a series of measurements that are close to one another and if the technique can differentiate properties that are close to one another, and not identical.
So a measuring technique can be accurate, precise, both accurate and precise, or neither.