Which of the following is the most precise instrument for measuring length?

Options

A. Meter rod of least count `0.1 cm`
B. Vernier callipers of least count `0.01 cm`
C. Screw gauge of least count `0.001 cm`
D. Data is not sufficient to decide

Explanation

To determine which of the following instruments is the most precise for measuring length, we need to compare their least counts. The least count is the smallest measurement that can be accurately read on the instrument, and a smaller least count indicates a more precise instrument.

### Step-by-Step Solution:

1. **Identify the Instruments**: We have three instruments to compare:
- Meter rod
- Vernier caliper
- Screw gauge (micrometer screw)

2. **Determine the Least Count of Each Instrument**:
- **Meter Rod**: The least count is 0.1 cm.
- **Vernier Caliper**: The least count is 0.01 cm.
- **Screw Gauge**: The least count is 0.001 cm.

3. **Compare the Least Counts**:
- The least count of the meter rod is 0.1 cm.
- The least count of the vernier caliper is 0.01 cm.
- The least count of the screw gauge is 0.001 cm.

4. **Identify the Most Precise Instrument**:
- The screw gauge has the smallest least count (0.001 cm), which means it can measure lengths with the highest precision.

5. **Conclusion**: Therefore, the most precise instrument for measuring length among the given options is the **screw gauge**.

### Final Answer:
The most precise instrument for measuring length is the **screw gauge**.

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