A vernier caliper is a tool used to measure the dimensions of an object's inside or outside, and also to measure depth (holes, gaps, etc.). This tool allows you to get more precise measurement results than you would get with a regular ruler/tape. This wikiHow teaches you how to use and read calipers.
Step
Part 1 of 2: Setting Up Equipment and Tools
Step 1. Understand the parts of the caliper
A caliper has a main/fixed jaw: the larger lower part is used to measure the outside diameter (or thickness) of the object, and the smaller jaw (upper part) is used to measure the inside diameter of the object. Some caliper models also have a depth gauge. The main scale remains in place, while the vernier scale (nonius scale) is a designation for a sliding scale that also functions to open and close the jaw.
Step 2. Read the scale on the caliper
Each scale on the caliper is read as it would on a regular ruler. Basically, a caliper has a main scale marked with a number in inches or centimeters, plus the smaller divisions between them. The sliding scale (vernier) should have a number mark on it to indicate the size of the scale that it represents.
- If no numbers are listed on the sliding scale, you can assume the parts of the number represent 1/10 of the smallest division on the main scale. For example, if the smallest line on the major scale represents 0.1 inches then each part of the number on the vernier scale represents 0.01 inches.
- The main scale is "original size," while the sliding scale is enlarged for easy reading. The magnification system allows the caliper to measure more precisely than a ruler.
Step 3. Check the scale of the smallest parts
Before making a measurement, count the number of lines between two numbers on the vernier scale. Use these lines to determine what size each smallest line represents.
For example, the number on the vernier scale indicates 0.1 inch, and there are five unnumbered lines in between. 0.1 inch 5 = 0.02 inch, so each unnumbered line represents 0.02 inch
Step 4. Clean the object to be measured
Wipe the object with a rag to ensure that there is no grease/oil adhering to it, and that there is nothing that would interfere with an accurate measurement.
Step 5. Unlock the screw
If your caliper has a locking screw, loosen it before you start measuring.
Rotating it to the right (clockwise) will tighten it, while turning it to the left (counterclockwise) will loosen it
Step 6. Close the jaws of the calipers
Before measuring anything, close your jaw and hold the reading at zero so you'll get the right size. Otherwise, when you take measurements you will not start with a scale that coincides with zero, and therefore you will have to correct for zero errors (zero error -measurement error due to the instrument's scale not being at zero).
- For example, if the zero on the sliding (vernier) scale coincides with 1 mm on the fixed (main) scale, you have a positive zero error i.e. +1 mm. Subtract 1 mm from all measurements to get the correct result.
- If the zero on the sliding scale is too far to the left of the zero on the main scale, you have a negative zero error. Shift the jaw so that it coincides with the zero, while paying attention to the number marks to see the size of the error. For example, if the 0.5 mm mark moves from the 1 mm figure approximately to the 2.1 mm position, the zero error is -(2, 1 - 1), or -1, 1 mm. Add 1.1 mm to all measurements to correct them.
Part 2 of 2: Using the Caliper
Step 1. Slide one of the jaws to clamp the object to be measured
The caliper has two types of jaws. The larger jaw clamps around the object, to measure its stretch/thickness. The smaller jaw is placed into the opening/hole of the object, then it can be pressed to measure the inside diameter (hole) of the object. You can adjust the jaw pair by sliding a smaller scale (sliding scale/ vernier/nonius). Once you have one of the jaws in position, tighten the locking screw if any.
Step 2. Read the main scale that coincides with the zero on the sliding scale
In principle, the main scale on a caliper shows a whole number plus the first decimal number (tenths). Read the measurement of zeros on the vernier sliding scale as you would a regular ruler.
- For example, if the zero (0) on the sliding scale aligns with the number 2 inches, your result is 2 inches. If the number coincides with 2 inches more than six tenths (6/10), your measurement will be 2.6 inches.
- If the result is between two lines, just use the smaller value. Do not attempt to estimate the value between the two lines.
Step 3. Read the vernier scale
Look for the first line on the vernier scale that coincides perfectly with any line on the main scale. The line shows the value of the additional digits.
- For example, the number 14 on the vernier scale coincides with a line on the main scale. Let's say the line represents an additional 0.01 inches. So, the number 14 represents 0.014 inches.
- This reading makes no difference which lines on the main scale coincide. We have taken readings from the main scale. So don't do another reading.
Step 4. Add the two numbers together
Add up the readings from the main scale and vernier scale to get the final answer. Make sure you use the correct units as listed on each scale. Otherwise, you will not get the correct answer.
- In our example, we measure 2.6 inches on the main scale, and 0.014 inches on the vernier scale. The final measurement result is 2,614 inches.
- The numbers are not always in a neat/precise line. For example, if the main scale in centimeters reads 0.85 and the 0.01 cm vernier scale reads 12, adding up the two will give 0.85 + 0.012 = 0.862 cm.
