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Accuracy and Precision watch

1. I am having a lot of trouble and am being baffled by the ideas of accuracy and precision in AS Physics - I understand the technical dartboard analogy, but I can't understand how that applies in real life. Here's an example of how it doesn't make sense to me:

"- When reading the extension from the ruler, we tried our best to look at it from the same angle in order to approve the precision of our measurements."

One part of me says this is a case of accuracy. If we are reading the ruler wrong, it will not be as close to the true value. But on the other hand, it could be precision as it would mean that the results are not repeatable as reading the ruler again would produce a different result.

How does it work? Can anyone dispell this confusion for me?
2. As I understand it, precision relates to the reproducability of a result using an identical method where as accuracy is something limited by the fundamental scale of the measuring device.

In the ruler example, precision is improved by reading it at the same angle each time as this improves the reproducability of the result. The accuracy of the ruler, on the other hand, is given by half the smallest marked unit on it (usually on a standard 30cm ruler) and is therefore independent of the angle you look at it.
3. Thank you. So do you think this would be reasonable?:

There are also some problems that will affect the accuracy of the experiment. Firstly, the ruler we used only had divisions of 1mm, when in some cases the extra extension on the wire when each weight is added may be less than this. Secondly, when we measure the diameter of the wire with the micrometer, the micrometer may not be measuring particularly close to the true value meaning that the cross-sectional area we find will not be entirely accurate. Thirdly, the weights may not measure exactly 100g each, which will again affect the results slightly, although this will probably not be significant.
4. precision = Rsults close to each other (small measuring scale)
Accuracy = Results close to their true value.
Its possible for results to be precise but not very accurate. For example a fancy piece of lab equipment may measure really precise results. But if its not calibrated properlly the results wont be accurate (close to true value!)
hope this is of help. :P
5. the ruler we used only had divisions of 1mm, when in some cases the extra extension on the wire when each weight is added may be less than this.
Good point, sounds reasonable to me.

Secondly, when we measure the diameter of the wire with the micrometer, the micrometer may not be measuring particularly close to the true value meaning that the cross-sectional area we find will not be entirely accurate.
If you're writing up an experiment, might also want to mention that the wire was measured at multiple points along its length and an average reading taken, to minimise any error due to it being of slightly non-uniform diameter along its length. I would also mention offset errors/zero errors/systematic errors (not sure which name you're using for them - they have many!) here, as you used a micrometer. You could say that they were dealt with (even if they weren't :-p) by (for example) saying something like:

Before any measurements were taken, the micrometer was zeroed according to the gauge and the offset recorded, to be subtracted from subsequent measurements.

Thirdly, the weights may not measure exactly 100g each, which will again affect the results slightly, although this will probably not be significant.
Fair point, doubt it was the largest source of error in the measurements - probably the measuring with the ruler was by the sounds of it!
6. (Original post by timROGERS)
I am having a lot of trouble and am being baffled by the ideas of accuracy and precision in AS Physics - I understand the technical dartboard analogy, but I can't understand how that applies in real life. Here's an example of how it doesn't make sense to me:

"- When reading the extension from the ruler, we tried our best to look at it from the same angle in order to approve the precision of our measurements."

One part of me says this is a case of accuracy. If we are reading the ruler wrong, it will not be as close to the true value. But on the other hand, it could be precision as it would mean that the results are not repeatable as reading the ruler again would produce a different result.

How does it work? Can anyone dispell this confusion for me?
I might be wrong but I think your interpreting it too much. It is as was said precision. You could use the same angle each time, and still get it wrong, because the angle itself is wrong, but your using a similar/same angle each time, therefore it is precise, but not necessarily accurate . Plus what you said about reading the ruler wrong is pretty meaningless, precision and accuracy refer to measurements and equipment. Precision is how small a measurement is, e.g. cm is more precise than m, and accuracy is how close to the true value. This experiment terminology is a load of bs if you ask me.
As I understand it, precision relates to the reproducability of a result using an identical method where as accuracy is something limited by the fundamental scale of the measuring device.
It's the other way around.
In the ruler example, precision is improved by reading it at the same angle each time as this improves the reproducability of the result.
Multiple readings, and taking an average, improves accuracy.
The accuracy of the ruler, on the other hand, is given by half the smallest marked unit on it (usually on a standard 30cm ruler) and is therefore independent of the angle you look at it.
This is precision.
8. accurate results are close to the true value

precise results have lots of decimal places but are not necessarily accurate

reliable results are repeatable

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