CA PLS Exam Preparation

Comprehensive preparation for the California Professional Land Surveyor (PLS) exam. Based on the January 2025 Test Plan with 6 modules and 57 topics. Content adapted from CalTrans LS/LSIT Video Exam Preparation Course materials.

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Lesson 2

Evaluating Historic vs. Measured Accuracy

Evaluating Historic vs. Measured Accuracy

Overview

Modern measurements are typically more precise than historical surveys. Understanding the accuracy of original surveys helps in proper interpretation and prevents inappropriate rejection of valid evidence.

Learning Objectives

  • Assess accuracy of historical surveys
  • Compare historical and modern precision
  • Apply appropriate tolerances
  • Avoid over-reliance on modern measurements

Key Concepts

Historical Survey Methods

Understanding original techniques:

  • Chain and compass surveys
  • Solar observation for direction
  • Simple theodolites and transits
  • Steel tape measurement
  • Proportionate measurement

Expected Accuracy

Typical historical precision:

  • Compass bearings: ±30 minutes to 1 degree
  • Chain distances: 1:2,500 to 1:10,000
  • PLSS original surveys: variable
  • Early California surveys: generally poor by modern standards

Modern vs. Historical Comparison

When comparing measurements:

  • Express differences in appropriate terms
  • Consider original survey limitations
  • Don't reject monuments based solely on measurement discrepancy
  • Evaluate pattern of errors

Proportional Considerations

Applying historical context:

  • Excess and deficiency distribution
  • Systematic vs. random errors
  • Relationship to controlling monuments

Key Terms

  • Precision: Refinement of measurement technique
  • Tolerance: Acceptable variation from expected value
  • Historical Accuracy: Typical uncertainty of period methods

Practice Questions

  1. What accuracy should be expected from a chain and compass survey?
  2. How does historical accuracy affect interpretation of found monuments?

Based on CalTrans LS/LSIT Video Exam Preparation Course materials.