# Zero Errors in Vernier Calipers and Micrometer Screw Gauge

1. Nov 6, 2013

### kunkun

Hi, I have a question to ask.
On my notes that my teacher gave me, he said that there are some errors in the notes. He had not responded to me which are the errors yet but he said about zero errors in vernier calipers and micrometer screw gauge.

The question is:
On my notes, it says that:

Vernier Calipers

1. Positive zero error occurs when the ‘0’ marking of the vernier scale appears after the ‘0’ marking of the main scale. The error is +x cm. To correct the reading, we subtract the error from the measurement.

2. Negative zero error occurs when the ‘0’ marking of the vernier scale appears before the ‘0’ marking of the main scale. The error is -(0.1-y) cm. To correct the reading, we subtract the error from the measurement.

Micrometer Screw Gauge

1. Positive zero error occurs when the ‘0’ marking of the thimble scale is below the horizontal reference line of the main scale. The error is +x mm. To correct the reading, we subtract the error from the measurement.

2. Negative zero error occurs when the ‘0’ marking of the thimble scale is below the horizontal reference line of the main scale. The error is -(0.1-y) mm. To correct the reading, we subtract the error from the measurement.

The problem lies in the sentence: To correct the reading, we subtract/add the error from the measurement.

About the subtracts in all the sentence, may I know which one should be add instead of subtract?

Thanks! :)

2. Nov 6, 2013

### Simon Bridge

When talking about errors it is important to use a clear language.
The word "error" can mean so many different things in science.

Your teacher was telling you that there are some mistakes in the text of the notes.
In the section on experimental uncertainty, it talks about systematic errors due to misplacement of the vernier scale. (The manufacturer mistakenly placed the vernier too high or too low.)

The misplacement of the vernier will make the reading too big or too small and you have to correct the measurement for that.

To know if you add or subtract, work out if the misplacement will cause the reading to be too big or too small.

3. Mar 9, 2015

### Laksh Arora

Error is always subtracted from the measurement but it is important to remember that the value of the error must be put with its sign. In positive zero error, the value is more than the actual measurement therefore on subtracting we get the actual value. In negative zero error, the apparent value is less than the actual value therefore on subtracting, the negative sign becomes positive and we obtain the real value. This concept is followed in other instruments also like screw gauge and spherometers.

4. Mar 9, 2015

### Laksh Arora

This concept removes the confusion of when to add or when to subtract. Just subtract the error with sign.

5. Mar 9, 2015

### Simon Bridge

Incorrect or misleading concepts often lend a sence of certainty.
This would be a poor treatment of statistical errors, mistakes, and systematic errors where the reading is too low. ( please see post #2 on different mmeanings of "error").

Note: "subtract ... with sign" does not mean anything. Perhaps English is a second language? It can trip you up like that.

6. Mar 25, 2016