This caliper with provided scales can measure up to about 7 inches and is accurate to about 5 thousandths of an inch.

The two halves slide on tracks and there are two rectangular pieces to hold the halves together and keep them pinched so that they won't slide free and lose your measurement. You wrap rubber bands around the rectangles as shown in the picture.

There are two .SVG files that hold the imagery for the Vernier scales. One is millimeters and the other is inches. I recommend printing the scales on adhesive label paper and then applying the scales as stickers to the calipers while the jaws are held closed. Make sure that the space between the main scale and the Vernier scale is placed along the line where the two halves slide against one another. Use an X-acto to slice the two slides free once the sticker is stuck down.

You can apply both scales. The millimeter scale is applied with the jaws to the left, pointing up. The inches scale is applied with the jaws to the left, pointing down.

The millimeter scale jumps by 2mm and then you add in the Vernier count* 1/3 mm.

The inches scale jumps by tenths and then you add in the Vernier count* 9/1000.

This project is also designed so that it can be run on a CNC mill starting with 5mm wood stock. If you have a laser, I would recommend lasering the scales onto the sides of the caliper.

This is a decent middle school science instrument that is reasonably accurate and reasonably precise for very little investment in time and materials.

Classroom lessons might deal with measuring common items as well as understanding the Vernier principles.