Transcript Measurements

Measurement
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Counting yields exact numbers
Measuring yields inexact values
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Always some error
Your job is to minimize it
Errors and Mistakes
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Errors - the difference between true
and measured values
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Tend to be small
Can be reduced, but not eliminated
Mistakes - blunders
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Cannot be compensated or averaged out
Can be eliminated by careful, consistent
work
Sources of Errors
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Instrument Errors
Natural Errors - caused by environment
Personal Errors - limits of surveyor’s
abilities
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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
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Systematic Errors
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Same magnitude and sign each time
Instrument errors, temperature effects
are systematic
Reduce by calculation
Random Errors
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As likely (+) as (-)
Usually small
Reduce by averaging
Personal errors are typically random.
Estimating Total Error
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Repeated Measurements
Etotal  E n
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Series of Unrepeated Measurements
Etotal  E  E  ...  E
2
1
2
2
2
n
Measurement
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Surveyors measure:
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Horizontal angles
Vertical angles
Horizontal distances
Vertical distances (elevations)
Slope distances
Significant Digits
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Carry 1 extra digit in calculations
Round off final answers
Surveyors typically measure
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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
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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.
Field Notes
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Legal Document
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Represent your work
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May end up in court
Sign, date each page
Neat, organized layout
Don’t obliterate mistakes - NO erasures
Use standard note forms
Field Note Rules
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Names and phone numbers on cover
Table of Contents
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Record measurements, not calculations!
Sketch where helpful
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Number pages together
Job title, Date, Page number
N arrow
Reference Points
Hard (3-H, 4-H) pencil, not pen
No Erasures
Field Note Pages
Job title
Date
Weather
Crew, ass’ns
Standard form
Signature