E-ink Ruler There are two main measuring units in the world: Metric and Imperial Units. Those two systems are totally different. Calculating the units is quite a handful. Based on this problem, we create a very convenient product called E-ink Ruler. There are four major features of E-ink Ruler. First, E-ink Ruler can change the unit immediately when consumers use it. Second, consumers can estimate the length of anything quickly. Third, it is very easy to divide a length into equal parts by adjusting E-ink Ruler’s Divide Button. Fourth, when it is circulated around a cylinder object, it can calculate the diameter and radius automatically.