No instrument is Correct

Mass (Weight)= 98.27grams

Length= 11.1cm

Speed= 60km/h

Temperature=37.0⁰ Celsius

Volume=43ml

Pressure Reading=0.00 Psig

“No Instrument is Correct”

Presented ByUsman Islam ( 2012-Ch-01 )

Metrology

Science of measurement. Embracing both experimental and theoretical determinations. Measurement is the process of determining Measuring instruments are measuring devices

“A measurement is not very meaningful without an error estimate”

Some Terminology

Absolutely Exact Value True value Measured value Error

Significant figures

Those digits in an observed quantity (measurement)

that are known with certainty plus the one

digit that is uncertain or estimated Depends on smallest division on a measuring tool

Example the ruler shown

reads 1.3 cm with

certainty and

1.35cm with

uncertainty.

Accuracy and Precision

Accuracy Precision – Reproducibility of results

Even if all the errors are neglected, the measurement’s accuracy of an instrument is limited by it’s Least Count

What is Least Count

The smallest value that can be measured by the measuring instrument is called its least count.

A measuring instrument can not measure any thing whose dimensions are less than the magnitude of least count

Measured values are good only up to this value The least count error will always be present in measurements

Least Count

For graduated scales calculated using the simple formula

Least Count= (Value Measured in “n” divisions) / (Number of divisions “n”)

Where n= Smallest divisions

Exercise: Determine the least count

Convincing Point The number “ π “ or “Pi” Circumference of circle=2πr Radius=r Diameter=2r The ratio of a circle's circumference to

its diameter.

First 100 digits of number “Pi”

3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679

References

http://www.chemteam.info/SigFigs/Measuring.html http://www.regentsprep.org/regents/math/algebra/am3/LError.html http://www.wikipedia.com http://www.miniwebtool.com/first-n-digits-of-pi/?number=100 http://www.slideshare.com http://merryquest.blogspot.com/2014/05/best-way-to-find-least-count-of.html

“Error does not mean blunder or mistake.

Rather it signifies accuracy.”