"We really liked our son's Lego ruler until he got half of his math homework wrong. It turns out over the length of the ruler, the ruler is off by a millimeter. This means when he did his assignment he measured 27.4 cm instead of 27.5 cm. He then rounded the wrong way (27 instead of 28) and got every answer based off this wrong. We definitely do NOT recommend this product as more than a cute novelty item. It is not functional. Needless to say we won't ever use it again."