Usage of vernier calipers

Do you know how to use a vernier caliper corectly to ensure your a precise measurement ? 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.