Select the correct statement(s) for a given vernier callipers, when the two jaws of the apparatus are in contact.

Options

A. If the zero of the vernier callipers, does not coincide with the zero of the main scale, then the vernier callipers is said to possess zero error.
B. Zero error and zero correction are same numerically, but opposite in sign.
C. Zero error is positive, when zero of the vernier scale lies to the left of the zero of the main scale.
D. Zero error is negative, when zero of the vernier scale lies to the left of the zero of the main scale.

Answer

To solve the question regarding the vernier calipers and the conditions when the two jaws are in contact, we need to analyze the statements provided and understand the concept of zero error in vernier calipers.

### Step-by-Step Solution:

1. **Understanding Vernier Calipers**:
- Vernier calipers are measuring instruments used to measure the dimensions of an object with high precision. They consist of a main scale and a sliding vernier scale.

2. **Contact Condition**:
- When the two jaws of the vernier caliper are in contact, we need to evaluate the position of the zero of the vernier scale relative to the zero of the main scale.

3. **Zero Error Concept**:
- Zero error occurs when the zero mark of the vernier scale does not coincide with the zero mark of the main scale when the jaws are closed. This misalignment can either be positive or negative.

4. **Positive and Negative Errors**:
- If the zero of the vernier scale is to the left of the zero of the main scale, it indicates a positive zero error. Conversely, if the zero of the vernier scale is to the right of the zero of the main scale, it indicates a negative zero error.

5. **Evaluating the Statements**:
- **Option A**: "The zero of the vernier scale does not coincide with the zero of the main scale of the vernier caliper is said to possess zero error."
- This statement is incorrect because it does not specify the nature of the zero error.
- **Option B**: "The zero error and zero correction are the same numerically but opposite in sign."
- This statement is incorrect because zero error and zero correction are not opposite in sign; they are the same in sign.
- **Option C**: "The zero error is positive when the zero of the vernier scale lies to the left of the zero of the main scale."
- This statement is correct as it accurately describes the condition for positive zero error.
- **Option D**: "Zero error is negative when the zero of the vernier scale lies to the left of the zero of the main scale."
- This statement is incorrect because it confuses the conditions for positive and negative zero errors.

6. **Conclusion**:
- The correct statement is **Option C**: "The zero error is positive when the zero of the vernier scale lies to the left of the zero of the main scale."