What is the disadvantage in comparing line segment by metre observation?

Explanation

### Step-by-Step Solution:

1. **Understanding the Concept**: When comparing line segments, we often use direct measurement methods like rulers or measuring tapes. However, the question asks about comparing line segments using mirror observation.

2. **Identifying the Method**: Mirror observation involves looking at the reflection of the line segments in a mirror to compare their lengths. This method can be misleading.

3. **Analyzing the Disadvantage**: The main disadvantage of using mirror observation is that it can create confusion. When two line segments are of almost the same length, it becomes difficult to determine which one is longer just by looking at their reflections.

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