If a precise measuring job is at hand, a Vernier caliper might be the tool for the job.

A caliper is a tool that measures inside dimensions, outside dimensions or depths of holes. Vernier caliper are considered the best tool for these types of jobs and are used by homeowners as well as scientists, educators and builders.

A very precise measuring instrument, the Vernier caliper has a reading error of .05 mm. For a job that needs a very specific and accurate measurement, this high accuracy is necessary.

Usage

To use a Vernier caliper, just close the jaws of the caliper lightly on the object you are measuring. If your object of measurement has a round cross section, make sure the axis of the item is perpendicular to the caliper. This step is necessary to guarantee that you're measuring the full diameter and not just a chord.

Once you have the Vernier caliper secured on the object you're measuring, ignore the top scale, which is calibrated in inches and instead use the bottom scale, which is in metric units.

Note that there is a sliding scale and a fixed scale. On the fixed scale of the Vernier caliper, note that the boldface numbers are in centimeters and the tick marks on the fixed scale (between the boldface numbers) are in millimeters.

There are ten tick marks on the sliding scale of the Vernier caliper. If you check the most left of the tick marks on the sliding scale, you can read from the fixed scale the number of whole millimeters that the jaws are opened.

Where to Buy

To purchase a Vernier caliper online, there are several sources. At www.lowes.com, you can purchase an economical Vernier caliper for less than $11. This caliper will measure up to 5" and provides a locking mechanism for repeat measuring.

At www.hardwarestore.com, you can also purchase a 5" Vernier caliper, the most popular choice for home use. Along with your caliper purchase, the company recommends other precise measuring tools like a pencil compass and scriber.

Vernier calipers can also be purchased online at www.amazon.com, where you can purchase 6 inch, 8 inch and 12 inch calipers. Amazon also offers digital Vernier calipers. Some auction sellers at Amazon offer the Vernier calipers at a slightly lower price than regular retail.