# Precision and Accuracy

When you are pulling out the plunger to 35, why is it important to make sure that the black line on the plunger is lined up with the 35 on the barrel?

There are actually two reasons. The first has to do with precision. When we talk about precision, we are talking about how consistently we are getting the same result when performing the same test over and over again. Another term for precision is “reproducibility.” As scientists, we are trained to be skeptical. That means that when you perform a test and publish the results, scientists all over the world are going to want to try your test for themselves to make sure they get the same result. That is why, when you write lab reports, it is important to give enough details in your procedures so that someone else can repeat exactly what you did.

So, if I am reading the 35 on the barrel at the black line on the plunger and someone else is reading the 35 at the very bottom of the plunger, then we will get different results.

Would it be okay if we all agreed to measure 35 at the very bottom of the plunger? It would be, if all we cared about was precision and reproducibility. As long as we all agreed, then we would get consistent results. However, the second reason why we want to make sure that the black line on the plunger is lined up with the 35 on the barrel is accuracy. The 35 means something. It is a measure of the volume inside of the syringe (we will discuss volume more thoroughly later in the unit). While we may not care about this now, we will later. And the syringe was designed so that when the black line on the plunger is lined up with the 35 on the barrel, the volume inside of the syringe is 35 milliliters (mL). If we measured 35 by lining up the very bottom of the plunger, then our measurement would not be accurate (the actual volume inside of the syringe would be greater than 35 mL).

Challenge: How can you tell that the syringe was designed to be read by the black line on the plunger?

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