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

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Presentation transcript:

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

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

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!

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.

Estimating Total Error Repeated Measurements Series of Unrepeated Measurements

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

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

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 when the true distance is represents good precision, but terrible accuracy.

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

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

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