Measurement

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 surveyors 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
• Dont 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
Field Note Pages