This is an excellent measuring device for the crafts person and for anyone who enjoys beading and jewelry making. The 12 " / 30 cm clear plastic ruler is designed specifically for beading work. The clear plastic design is very useful, it allows you to lay the ruler and its other built in gauges on top of the work piece so you do not have to try to align it up along the edge which can be difficult in some situations. Along with the standard inch and cm measures, the ruler incorporates a bead diameter gauge, allowing you to check and compare the diameter of beads from 2-20 mm, and also features a beads per inch gauge for beads 2-10 mm in size. This allows you to estimate the amount of beads, pearls or other round stones you will need for a necklace, bracelet or other project.