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Episode 2 Measurements

It this post I talk about measurements.

The first question is how accurate do you need to be.   You have to determine that because absolute accuracy is not always necessary.

After that I discuss things that decrease accuracy.   Most of the time inaccuracy is due to technique and not a problem with the tool.

When measuring volume and many other things always choose a measuring device slightly larger than the amount of material that you want to measure.  In the case of volume measurements this means the measuring device is a smaller diameter and changes in the volume will cause a greater effect on the height of the material in the measuring device. It can be said that the measuring device is more sensitive and therefore more accurate.

Other sources of inaccuracy related to technique is not shaking a powder material in the measuring cup so you are looking at a flat surface.  Another source of inaccuracy is looking at a gauge at an angle instead of straight on.  This creates an error called parallax error.

The term repeatability is introduced.  This basically means being consistently the same on how you take the measurement so the measurement number means the same thing today as it does tomorrow.

In length measurements, it is always best to not trust the end of the ruler, or measuring tape.  It is much better to start at some mark (for example 1 foot or 1 inch) and subtract this from the measurement at the other end.

A copy of these notes and some pictures can be found here in pdf format:  episode 2 notes

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