Straightedge vs Ruler

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About This Diagram

This comparison diagram explains the fundamental difference between a ruler and a straightedge, and why classical geometric constructions use only a straightedge.

Key Differences

Tool	Markings	Use in Constructions
Ruler	Has numbered measurements	✗ NOT allowed
Straightedge	No markings	✓ USED

Why the Distinction Matters

Rulers rely on numerical measurements which: - Depend on arbitrary units (inches, cm, etc.) - Cannot express pure geometric relationships

Straightedges can only: - Draw lines through two given points - Create relationships based on geometry, not numbers

How to Use

1. Hover over each panel to highlight that tool
2. Compare the explanations for why one is allowed and one isn't
3. Notice the straightedge is used to draw a line through points A and B

Learning Objectives

• Understand the difference between a straightedge and a ruler
• Analyze why constructions use straightedges instead of rulers
• Recognize that geometric relationships are independent of measurement units

Bloom's Taxonomy Level

Understanding and Analyzing - Distinguishing between tools and their purposes.

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