What is the disadvantage in comparing line segments by mere observation?

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the disadvantages of comparing line segments just by looking at them without any measuring tools.

2. **Identifying the Issue**: When two line segments are almost equal in length, it becomes difficult to determine which one is longer or shorter just by observation.

3. **Example Illustration**: Consider two line segments, A and B. If A is slightly longer than B, but the difference is very small, it may not be easily noticeable when you look at them.

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