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Precision Measurement Fundacións of Engineering and Technology
PRECISION MEASUREMENT
“When measured quantities are reported, the last significant digit in a measurement
is somewhat uncertain.”
- Park (1996)
PRECISION MEASUREMENT
• Must take into consideration
• Significant digits• Units• What is being measured
• Energy
• Power
• Length
• Weight
ROUNDING• Look at the number to the immediate right of the place you
are rounding to:
• If it is greater than 5 (i.e. 6,7,8, or 9), round the place of interest up
• If it is less than 5 (i.e. 0,1,2,3, or 4), leave the place of interest unchanged
• If is if 5• Round up by one if there are any non-zero digits following
5
• If there are only zeros following the 5, round up by one if the place of interest is odd, if its even leave it unchanged
ROUNDING
• Let’s practice with (3.141592653589)
• Round to 4 decimal places• 3.1416
• Round to 2 decimal places• 3.14
• Round to 3 decimal places• 3.142
• Round to 7 decimal places • 3.1415927
SIGNIFICANT DIGITS• Non-zero digits are always significant
• 523.7 4 significant figures• Any zeros between two significant digits are
significant
• 23.07 4 significant figures• A final zero or trailing zeros in the decimal portion
ONLY are significant
• 3.200 4 significant figures• 200 1 significant figure• 2.00 x 102 3 significant figures
• Leading zeros in a number are not significant• 0.0075 2 significant figures
SIGNIFICANT DIGITS• Let’s take another look at rule number 3…
• Does 1000 ml mean exactly 1000?
• Not necessarily• 1000, 100, 10, and 1 all have one significant digit
• If the engineer wanted to express exactly 1000, what would they need to write?
• 1.000 x 103
SIGNIFICANT DIGITS
SIGNIFICANT DIGITS
UNITS OF MEASUREQuantity English Unit SI Unit Conversion
Length
Inch (in) Centimeter (cm) 1 in = 2.54 cm
Foot (ft) Meter (m) 1 ft = 0.3048 m
Mile (mi) Kilometer (km) 1 mi = 1.609 km
Mass Pound Mass (lbm) Kilogram (kg) 1 lbm = 0.4536 kg
Force Pound Force (lbf) Newton (N) 1 lbf = 4.448 N
TemperatureFahrenheit (TF) Kelvin (TK) TK = 5/9 x (TF – 32) +
273.15
Pressure
Pound per square inch (psi)
Pascal 1 psi = 6.895 x 103 Pa
Atmosphere (atm) Pascal 1 atm = 1.013 x 102 Pa
PowerBtu/hr Watts (W) 1 Btu/h = 0.2929 W
Horsepower (hp) Watts (W) 1 hp = 745.7 W
Magnetic fieldGauss (gauss) Telsa (telsa) 1 gauss = 1.000 x 10-4
telsa
UNITS OF MEASUREQuantity English Unit SI Unit Conversion
Time Seconds (sec)
Volume
Cubic Foot (ft3) Cubic Meter (m3) 1 ft3 = 0.02832 m3
Cubic Inch (in3) Cubic Meter (m3) 1 in3 = 1.6387 x 10-5 m3
Gallon (gal) Cubic Meter (m3) 1 gal = 3.785 x 10 -3 m3
Velocity Miles per hour (mph) Meters per second (m/s) 1 mph = 0.4470 m/s
Area
Square Inch (in2) Square Centimeter (cm2) 1 in2 = 6.452 cm2
Square Foot (ft2) Square Meter (m2) 1 ft2 = 0.0929 m2
Square Mile (mi2) Square Kilometer (km2) 1 mi 2 = 2.590 km2
Angle Degree () Radians (radian) 1 = /180 = 0.01745 rad
For more conversions visit http://www.digitaldutch.com/unitconverter/energy.htm
PRECISION VS. ACCURACY • Precision
• Refers to how close together a series of measurements are to each other
• Accuracy
• Refers to how close a measured value is to an accepted value
PRECISION AND ACCURACY??
PRECISION AND ACCURACY??
PRECISION AND ACCURACY??
FOR ADDITIONAL EXPLANATION
https://www.youtube.com/watch?v=b38hFWvEjwI