A metre scale is graduated at every millimetre. How many significant digits will be there in a length measurement with this scale?

Explanation

To determine the number of significant digits in a length measurement using a meter scale graduated at every millimeter, we can follow these steps:

### Step 1: Understand the Scale Graduations
A meter scale graduated at every millimeter means that the smallest division on the scale is 1 mm. This indicates that measurements can be made to the nearest millimeter.

### Step 2: Identify the Measurement Precision
Since the scale is marked in millimeters, any measurement taken can be precise to 1 mm. This means that if you measure a length, you can confidently report it to the nearest millimeter.

### Step 3: Determine Significant Digits
1. **Whole Number Measurements**: If you measure a length and it reads, for example, 5 mm, this has **1 significant digit**.
2. **Two-Digit Measurements**: If the measurement is 55 mm, it has **2 significant digits**.
3. **Three-Digit Measurements**: If the measurement is 222 mm, it has **3 significant digits**.
4. **Four-Digit Measurements**: If the measurement is 2222 mm, it has **4 significant digits**.

### Step 4: Conclusion
The number of significant digits in a measurement taken with this scale depends on the value measured. However, since the scale allows measurements to the nearest millimeter, the maximum number of significant digits you can achieve is **4** when measuring a length up to 9999 mm (or 9.999 m).

### Final Answer
Thus, the maximum number of significant digits in a length measurement with a meter scale graduated at every millimeter is **4**.

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