Comment by ctdavies | Hacker News Reader

Comment by ctdavies | Hacker News Reader

I'm confused by the use of "accuracy" and "precision" in this article.

From the IEEE article: "[ultranarrow lasers] will make it practical for us to achieve an accuracy below 10^-18–more than 100 times the precision of cesium clocks."

From http://en.wikipedia.org/wiki/Accuracy_and_precision: "accuracy is the proximity of measurement results to the true value; precision, the repeatability, or reproducibility of the measurement."

Am I mistaken, or is the IEEE article conflating accuracy and precision?

Here's the most precise clock in the world:

    2014-10-03 00:00:00.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

It's just not very accurate.

In this case, precision is a prerequisite for accuracy, so it's implicit that higher accuracy involves greater precision.

Ah I see. Thanks for clearing that up.

In general, when talking about a class of measuring device, the expected accuracy of the measure cannot exceed its expected precision (the converse is not true, however.)

That is, the expected difference between two randomly selected devices in the class attempting to measure the same true value is a lower bound on the expected difference between the measurement of one device in the class and the true value.

Or, looked at a different way, if you can't shoot a tight grouping (independent of where on the target it clusters), you can't shoot a tight grouping around the bullseye.

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