How to Measure with a Vernier Caliper

How to use a vernier caliper.

A vernier caliper precisely measures any object. It can measure an object to within +/- .05mm accurately. A vernier caliper contains three measuring devices in one tool. They are commonly found not only in laboratories and classrooms but also in the workplace. Even automotive mechanics can use vernier calipers to measure parts like brake rotors and engine cylinders.

Get to Know the Vernier Caliper

A vernier caliper has two sets of jaws and a sliding ruler. One set of jaws measures an object's internal measurements. An example would be the inside distance between a pipe's walls. The other set of jaws measures an objects outside dimensions. The depth ruler slides out the vernier caliper's end on the opposite side of its jaws. All whole number measurements are taken on a slide ruler that runs along one side of the caliper. The bold face numbers on the ruler are centimeters and the dash marks are millimeters. A vernier caliper uses a fine tuning adjustment screw, which is located below the slide rule. A locking screw, located on top, locks the ruler in place after the fine tuning has completed.

All measurements should be completed with the object held a perpendicular angle to the Vernier caliper. Otherwise, in the case of a round object, the measurement would be a chord. A chord is any measurement taken across a round object that is not its diameter. The jaws should grip the object lightly.

Using a Vernier Caliper

Loosen the vernier caliper's locking screw. Place one edge of the object against the flat part of the vernier caliper's fixed jaws. The fixed jaw connects to the end of the ruler and lines up with the zero measurement mark. Outside measurements use the larger jaws found on the bottom of the ruler and have the flat part of the jaws facing each other. Inside measurements use the smaller jaws located on top of the ruler and have the flat part of the jaws facing out. Close the vernier until the flat part of the sliding jaw nearly touches the object. Keep the sliding jaw off of the object. Turn the Vernier caliper's fine adjustment wheel until the jaws lightly touch the object. Do not over tighten the screw or bind the jaws. This will give false readings. Tighten the locking screw and remove the vernier caliper from the object.

Read the Vernier Caliper

Find the fine tuning tick-mark that reads zero. Follow that mark up to the ruler. Read the whole number measurement above this tick mark. If the zero mark lines up between two numbers, then use the smaller number as the whole number. Record this number. Next find the object's tenths of millimeters measurement. The ten tick marks on the sliding scale are the same width as nine ticks marks on the fixed ruler. This means that at most one of the tick marks on the fine-tuning scale will align with a tick mark on the fixed ruler. Find the tick mark that lines exactly with the ruler's mark. Count from the zero tick-mark to the one that lines up with the ruler's mark. This number represents the number of tenths of millimeters.

An example would be; if the fine adjustment ruler's zero mark ends up between 45 and 46 millimeters and the sixth fine tuning tick mark lines up with a millimeter mark on the ruler, then the exact measurement would be 45.60 +/- .05 mm. Remember the vernier caliper only reads to within +/-.05mm.


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