Reading an inch caliper involves combining the measurements from the main scale and the Vernier scale to get a precise dimension.
Understanding the Inch Caliper Scales
An inch caliper typically has two main parts for measurement: the main scale and the Vernier scale (also called the sliding scale).
The Main Scale
The main scale is fixed to the caliper body and is marked in inches. Based on the reference, on an inch Vernier caliper:
- Each major numbered increment represents a whole inch.
- Between the whole inch marks, there are smaller increments. Each of these larger increments on the main scale represents one-tenth (0.1) of an inch. These might be labelled 0, .1, .2, .3, etc., after each whole inch mark.
- Between each tenth of an inch mark, there are smaller divisions. Each of these divisions represents twenty-five thousandths (0.025) of an inch. There are typically four such divisions between each tenth mark (.1, .2, etc.), as 4 * 0.025 = 0.1.
The Vernier Scale
The Vernier scale is marked on the sliding jaw. It allows you to measure fractions of the smallest main scale division (0.025 inch), typically providing precision down to the thousandths or ten-thousandths of an inch. By finding which line on the Vernier scale aligns perfectly with a line on the main scale, you determine the final digits of your measurement.
Step-by-Step Guide to Reading an Inch Caliper
Here is how to read a measurement using an inch Vernier caliper:
- Close the Jaws: Ensure the caliper jaws are clean and properly closed, or place the object you want to measure between the jaws.
- Read the Main Scale: Look at the zero line on the Vernier scale.
- Identify the last whole inch mark on the main scale that the Vernier zero line has passed.
- Identify the last tenth-of-an-inch (0.1) mark on the main scale that the Vernier zero line has passed after the last whole inch mark. (Remember, each main scale increment is 0.1 inch).
- Count the number of smaller twenty-five thousandths (0.025) of an inch divisions on the main scale that the Vernier zero line has passed after the last tenth mark.
- Read the Vernier Scale: Look along the lines of the Vernier scale to find the line that aligns perfectly with any line on the main scale.
- Read the value corresponding to this aligned line on the Vernier scale. This value represents the thousandths (or ten-thousandths) part of your measurement.
- Add the Readings: Sum the values obtained from the main scale and the Vernier scale to get the total measurement.
- Total Measurement = (Whole Inches) + (Tenths) + (Number of 0.025 Divisions * 0.025) + (Vernier Scale Reading)
Example Reading
Let's assume the Vernier zero is past:
- The
1 inchmark. - The
.3tenth mark (representing 0.3 inches). - Two
0.025divisions after the.3mark (representing 2 * 0.025 = 0.050 inches). - The
0.012line on the Vernier scale aligns perfectly with a main scale line (representing 0.012 inches).
The reading would be calculated as follows:
| Component | Value (Inches) |
|---|---|
| Whole Inches | 1.000 |
| Tenths (.1 increments) | 0.300 |
| 0.025 Divisions | 0.050 |
| Vernier Alignment | 0.012 |
| Total Reading | 1.362 |
Therefore, the measurement is 1.362 inches.
By following these steps and understanding the values represented by the divisions on both the main and Vernier scales, you can accurately read an inch caliper.
