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Measuring Accuracy v. Precision pg. 8 Precision - how closely the measurements match each other. Instruments that measure using more decimals are more precise. Accuracy – how closely the measurement matches the true or accepted value. Accurate Precise Accurate Precise Accurate Precise Accurate Precise Accurate Precise How To Read Scientific Instruments • 1) Record the _______ digit on the instrument. • 2) Then _______________ the last digit. How to Count Significant Figures 1. Count all of the digits you are sure of. 2. Add the last digit you estimate. Percent Error • When quantities have accepted or true values, we can calculate the percent error between our measurement of the value and the accepted value with the formula How to Read a Graduated Cylinder • Sit the graduated cylinder on a level surface. • Lower your eyes to the level of the liquid (called the meniscus). • Take your reading from the bottom of the meniscus. • Count all of the digits you are sure of. • Add the last digit that you estimate. Quiz • Number your paper 1 to 15. 1) Measuring Length A. B. C. D. 2 cm 19 cm 1.95 cm 1.95238 cm 2) Measuring Length A. B. C. D. 10cm 1.1cm 1.05cm 1.526cm 3) Measuring Length A. B. C. D. 17 cm 17.5 cm 18.0 cm 17.5082 cm 4) Measuring Length A. B. C. D. 4cm 4.3cm 4.30cm 4.3057cm 5) Measuring Length A. B. C. D. 12 cm 12.0 cm 12.7 cm 12.0953 cm 6) Measuring Liquids • The meniscus is the curve in the upper surface of a liquid close to the surface of the container or another object, caused by surface tension. It can be either convex or concave. Is this meniscus convex or concave? 6) _________________ For questions 7 to 12, measure the amount of liquid in each graduated cylinder by reading the bottom of the meniscus. 7) Measuring Liquid Volume A.10ml B.10.3ml C. 11.5ml D.13.0ml 8) Measuring Liquid Volume A. B. C. D. 266 ml 287 ml 290 ml 294 ml 9) Measuring Liquid Volume A.52 ml B.53 ml C. 54.5 ml D.52.8 ml 10) Measuring Liquid Volume A.80 ml B.80.0 ml C. 81.0 ml D.79.0 ml 11) Measuring Liquid Volume A.2.8 ml B.2.80 ml C. 2.90 ml D.2.9 ml 12) Measuring Liquid Volume A.4.90 ml B.4.80 ml C. 5.0 ml D.5.0853 ml 13) Measuring Solids A.625.62g B.26.57g C.265.73 D.526.6g 14) Measuring Solids A.373.33g B.734.33g C.374.33g D.373.3g 15) Measuring Solids A.222.50g B.221.50g C.221.5g D.221.0g