Return on investment (ROI) or return on costs (ROC) is a ratio between net income (over a period) and investment (costs resulting from an investment of some resources at a point in time). A high ROI means the investment's gains compare favourably to its cost. As a performance measure, ROI is used to evaluate the efficiency of an investment or to compare the efficiencies of several different investments. In economic terms, it is one way of relating profits to capital invested. Purpose In business, the purpose of the return on investment (ROI) metric is to measure, per period, rates of return on money invested in an economic entity in order to decide whether or not to undertake an investment. It is also used as an indicator to compare different investments within a portfolio. The investment with the largest ROI is usually prioritized, even though the spread of ROI over the time period of an investment should also be taken into account. Recently, the concept has also been applied to scientific funding agencies’ (e.g., National Science Foundation) investments in research of open source hardware and subsequent returns...