Quote:
Originally Posted by srivendel
I don't even really care if it's inaccurate, as long as it is consistently inaccurate in the same way. In other words, if the results are reproducable, then it's useful, because performance mods should influence the numbers, even if the absolute number is wrong.
S.
That would be called a "high level of precision". Accuracy is a measure of an instrument's ability to produce results that are consistent with a known standard, while precision is a measure of an instrument's ability to reproduce similar results repeatedly. While the two terms are commonly used interchangeably, they do
not mean the same thing, at least from a scientific point of view.
You can have an instrument with a high level of accuracy that has horrible precision. You can also have a high level of precision with horrible accuracy. For example, let's say you measure the air pressure of a static vessel at 32psi with two pressure gauges. Gauge #1 give you three readings - one of 28psi, one of 32psi, and one of 36psi. The average of the three readings is 32psi, which is an accurate result. However, gauge #1 offers horrible precision, since it does not produce repeatable readings.
On the other hand, gauge #2 give you three readings, all of which are 37psi. Gauge #2 is inaccurate, but offers a high level of precision. A precise instrument can be used effectively by calibrating it against a known standard (in this example, I know it reads 37psi when measuring 32psi of pressure, so in the future I can reasonably assume that a reading of 37psi corresponds to a real pressure of 32psi). An accurate but imprecise instrument is much harder to make effective observations with.
FWIW, I agree on your assessment that for measurements of change (like the effectiveness of mods), being able to determine an accurate reading isn't as important as being able to produce precise readings. For instance, I've used a crappy little $2 air pressure gauge for years to measure tire pressures. Are the readings it produces accurate - I.e., if it reads 32psi, is there
really 32psi in the tires? I don't know, and I don't really care. What does matter to me is that when it reads 32psi, the tire pressure is identical (for practical intents and purposes) to what it was the last time it read 32psi. The repeatability of the readings is more important to me in this instance than the accuracy.