If the sliding scale doesn’t have a label, you can assume the numbered divisions represent 1/10 of the smallest division on the main scale. For example, if the main scale’s smallest lines represent 0. 1 inches, then each numbered division on the Vernier scale represents 0. 01 inches. The main scale is “life size,” while the sliding scale is magnified for easy reading. This magnification system allows the Vernier caliper to measure more precisely than a ruler.

For example, the numbers on a Vernier scale represent 0. 1 inches, and there are five unnumbered lines between them. 0. 1 inches ÷ 5 = 0. 02 inches, so each of the unnumbered lines represents 0. 02 inches.

Twisting something to the right (clockwise) will tighten it, while twisting it to the left (counter clockwise) will loosen it.

For example, if the zero on the sliding scale lines up with 1 mm on the fixed scale, you have a positive zero error of +1 mm. Subtract 1 mm from all measurements to get the right result. If the zero on the sliding scale is to the left of the main scale zero, you have a negative zero error. Slide it so the zeros line up, while watching another mark to see the size of the error. For example, if the 0. 5mm mark moves from the 1mm mark to about 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 this.

For example, if the 0 on the sliding scale lines up with the 2 inch mark, your measurement is 2 inches. If it lines up past 2 inches by six tenth-inch marks, your measurement is 2. 6 inches. If the result is between two lines, just use the smaller value. Do not try to estimate a value between the two lines.

For example, the 14 on the Vernier scale aligns with a line on the main scale. Let’s say the scale represents 0. 01 inch increments, so the 14 represents 0. 014". It makes no difference which line on the main scale it aligns with. We’ve already taken our reading from the main scale; don’t take another one.

In our example, we measured 2. 6 inches on the main scale, and 0. 014 inches on the Vernier scale. Our final measurement is 2. 614 inches. The digits don’t always line up this neatly. For example, if the main centimeter scale reads 0. 85, and the Vernier 0. 01 cm scale reads 12, adding them together results in 0. 85 + 0. 012 = 0. 862 cm.