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Zero out the calipers before you get started. Clamp the jaws around the outside of the object for an external measurement. Open the jaws inside of an object to find the inner diameter. Push the extension rod into the object for a depth measurement. Look at the digital reading.
Slide the clamps closed and push the extension rod in all the way. Then, hit reset to display only zeros on the screen. Properly zeroed calipers are essential to getting an accurate measurement, so make sure to do this! Calipers have 2 large jaws that you can open and close around the outside of an object. These jaws are located at the bottom of the ruler part of the calipers. Open the calipers so they are wider than the outside of the object, and then close the calipers around the part of the object you want to measure. For example, to measure the length of a nail, open the calipers wider than the length of the nail and close them so that 1 jaw is touching the head of the screw and the other is against the pointed end of the screw. Find the inner measurement jaws on top of the calipers (above the part that looks like a ruler). These are smaller than the outer jaws. Close the inner jaws of the calipers and put them inside of the object. Open the calipers so the inner jaws are pressed against the inside of the object. For example, to measure the inner diameter of a pipe, open the calipers until they are pressed against the inside of the pipe to get your measurement. Locate the extension rod on the side (or end of the ruler section) of the calipers. Position the calipers against the top edge of the object or hole, and then extend the bar down into the hole or object until it touches the bottom. For example, to measure the depth of a hole, place the caliper jaws against the rim of the hole and extend the bar down into the hole all the way to the bottom. Look at the screen and record the number. Keep in mind that the readout will include a zero or whole number followed by a decimal and 3 digits behind it.  For example, the readout may say 0.365 in (0.93 cm) or 4.987 in (12.67 cm). Record the entire number as your measurement. Some digital calipers have a button to change the measurement from imperial to metric or vice versa. Check to see if this is a feature of your calipers and press the button if needed.