Under what circumstances could a series of measurements of the same quality be precise but inaccurate?

Question

Under what circumstances could a series of measurements of the same quality be precise but inaccurate?

Answer 1

Well a simple answer is in the theory of "Electricity". Dealing in "Ohm's Law" this type of question could be answered. Take a simple series circuit for instance. Depending on which formulas you use you will get different answers all of them precise but all within a whole number of themselves.  I guess thats why they call it "Theory of Electricity."

Answer 2

Tolerance.  If a piece of pipe is cut to 25 feet, say, there could be up to 1/2 inch or more difference over that 25 feet (some under, but we'll 'discard' those as being 'too short') ... then the piece is measured again and is 'cut to tolerance' of let's say 1/100th of a inch.  NOTHING can be cut 'exactly' to specifications every time, so the 'precision' has 'tolerance levels' ... I know this because I was married to a man who cut fuel pipe for the space shuttles ... there was 1/1000th of an inch 'tolerance' in a 25' long piece of pipe, and this man was such a 'nit-picker' that only one in every 50 'cuts' was 'thrown out' to be used in other ways ... first cut accuracy is extremely rare but it does happen occasionally.

Answer 3

Under what circumstances could a series of measurements of the same quality be precise but inaccurate?

Probably the most common cause is taking the measurements when the ambient temperature is hotter or colder than the normal operating conditions for where the circuitry is or will be located.

Example - If I was a technician taking measurements on a piece of equipment that was destined to be operated outdoors in a very cold climate, I would not take the measurements at room temperature inside of a building.

Answer 4

yes-totally possible

please note:

precision refers to how close the measuring instrument is to the standard of measurement (a value that every one agrees on to be the official size of said unit)

were as accuracy measures how well something was measured, mainly in terms of how many significant digits there are (how closely it was measured ie. to the tenths place is less accurate than to the hundredths place)

so in your question, this would be accomplished by having a very precise instrument for measuring, however either not measured to the most accurate decimal place (the smaller the better) or perhaps even poorly measured

enjoy your new found measuring skills

but if all else fails

go to

http://en.wikipedia.org/wiki/Accuracy

and

http://www.chem.tamu.edu/class/fyp/mathr...

and

http://www.physics.uoguelph.ca/tutorials...

Answer 5

Pretend you have a 1 foot ruler which is acutally 1.002 ft long. You measure some stuff at "precisely" 1.000 ft. All your measurment are precise and of the same quality but they are all innacurate, ie they are all .002 ft in error.

Answer 6

many factors,, your question is too blague to  give a PRECISE answer, add more info  examples

Answer 7

when two different people measure it and use different starting points

Answer 8

Let's say you are measuring the distance from State and Madison in Chicago to 42nd and Broadway in NY City, using your car's odometer as the measuring device.

You make 5 round trips over the same roads and do not drive off of the route.

One-way results:

866.7 miles

867.0

867.1

866.8

866.7

866.9

867.0

867.3

867.0

866.8

This give an average of 867.0 miles.

The results are fairly precise, given the long distance involved.  That is, they are all pretty close to one another; all within 0.3 miles of the mean.

But your tires on your car are old; they had 45,000 miles on them when you began measuring.  This means that your odometer is not measuring a mile accurately.  The diameter of the worn tire is much less than it was when the car was new, so the tire is making more revolutions per mile that it did originally when it was accurate.  More revolutions means a higher reading in the mileage than the actual mileage.   The actual distance may be closer to 850 miles.

So, even though your measurements are precise, they are inaccurate.

PRECISION:  a set of data consistent or repeatable.

ACCURACY: a set of data that matches the true condition.

Answer 9

One example would be when the measurement tool was calibrated incorrectly, resulting in repeatable measurements that are centered at the wrong value.

Answer 10

Good question. This will demonstrate the difference between precision and accuracy. A guy throws 10 darts at the board. One hits the bullseye, the rest are scattered. Truely, a random pattern. He is not precise nor accurate.

Next guy hits 10 darts on the bullseye. He is both accurate and precise.

Next guy hits all 10 darts 2inches left of the bullseye. He is precise but not accurate.

So on a measurement, if you know it is not accurate but off by a known amount, it still can be precise but not accurate. So, you may still use these measurements.

Remember, a stopped clock is not precise, but accurate twice a day.