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  ( ) Round to 4 decimal places Round to 2 decimal places 3.14 Round to 3 decimal places Round to 7 decimal places

SIGNIFICANT DIGITS Non-zero digits are always significant  4 significant figures Any zeros between two significant digits are significant  4 significant figures A final zero or trailing zeros in the decimal portion ONLY are significant  4 significant figures 200  1 significant figure 2.00 x 10 2  3 significant figures Leading zeros in a number are not significant  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? x 10 3

SIGNIFICANT DIGITS

UNITS OF MEASURE QuantityEnglish UnitSI UnitConversion Length Inch (in)Centimeter (cm)1 in = 2.54 cm Foot (ft)Meter (m)1 ft = m Mile (mi)Kilometer (km)1 mi = km Mass Pound Mass (lbm)Kilogram (kg)1 lbm = kg Force Pound Force (lbf)Newton (N)1 lbf = N Temperature Fahrenheit (T F )Kelvin (T K )T K = 5/9 x (T F – 32) Pressure Pound per square inch (psi) Pascal1 psi = x 10 3 Pa Atmosphere (atm)Pascal1 atm = x 10 2 Pa Power Btu/hrWatts (W)1 Btu/h = W Horsepower (hp)Watts (W)1 hp = W Magnetic field Gauss (gauss)Telsa (telsa)1 gauss = x telsa

UNITS OF MEASURE QuantityEnglish UnitSI UnitConversion Time Seconds (sec) Volume Cubic Foot (ft 3 )Cubic Meter (m 3 )1 ft 3 = m 3 Cubic Inch (in 3 )Cubic Meter (m 3 )1 in 3 = x m 3 Gallon (gal)Cubic Meter (m 3 )1 gal = x m 3 Velocity Miles per hour (mph)Meters per second (m/s)1 mph = m/s Area Square Inch (in 2 )Square Centimeter (cm 2 )1 in 2 = cm 2 Square Foot (ft 2 )Square Meter (m 2 )1 ft 2 = m 2 Square Mile (mi 2 )Square Kilometer (km 2 )1 mi 2 = km 2 Angle Degree (  ) Radians (radian) 1  =  /180  = rad For more conversions visit

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??

FOR ADDITIONAL EXPLANATION