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Measurement

Understand the importance of minimizing errors in surveying measurements, the difference between errors and mistakes, and how to estimate total error. Learn about significant digits, accuracy, precision, and the importance of detailed field notes.

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Measurement

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  1. Measurement • Counting yields exact numbers • Measuring yields inexact values • Always some error • Your job is to minimize it

  2. Errors and Mistakes • Errors - the difference between true and measured values • Tend to be small • Can be reduced, but not eliminated • Mistakes - blunders • Cannot be compensated or averaged out • Can be eliminated by careful, consistent work

  3. Sources of Errors • Instrument Errors • Natural Errors - caused by environment • Personal Errors - limits of surveyor’s abilities • Recording 3.91 when the true reading was 3.90 might be a personal error. • Recording 4.91 when the true reading is 3.90 is a mistake - redo!

  4. Systematic vs. Random Errors • Systematic Errors • Same magnitude and sign each time • Instrument errors, temperature effects are systematic • Reduce by calculation • Random Errors • As likely (+) as (-) • Usually small • Reduce by averaging • Personal errors are typically random.

  5. Estimating Total Error • Repeated Measurements • Series of Unrepeated Measurements

  6. Measurement • Surveyors measure: • Horizontal angles • Vertical angles • Horizontal distances • Vertical distances (elevations) • Slope distances

  7. Significant Digits • Carry 1 extra digit in calculations • Round off final answers • Surveyors typically measure • Feet to .01’ • Meters to .01 m = 1 cm • Angles to limits of instrument: 1’ up to 1” • Record results that show limits

  8. Accuracy and Precision • Accuracy - how close your measured values come to the actual or true values. • Precision - how well you can repeat your measurements. • Measurements of 90.03, 90.02, and 90.03 when the true distance is 100.00 represents good precision, but terrible accuracy.

  9. Field Notes • Legal Document • May end up in court • Sign, date each page • Represent your work • Neat, organized layout • Don’t obliterate mistakes - NO erasures • Use standard note forms

  10. Field Note Rules • Names and phone numbers on cover • Table of Contents • Number pages together • Job title, Date, Page number • Record measurements, not calculations! • Sketch where helpful • N arrow • Reference Points • Hard (3-H, 4-H) pencil, not pen • No Erasures

  11. Job title Date Weather Crew, ass’ns Standard form Signature Field Note Pages

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