It is not longer necessary to prove that the International System of Units (SI) is a fact. It is normally used in schools and universities. Scientists systematically use SI in their publications. New books and databases are commonly built on it. Meanwhile, some industries (oil companies among others) keep on using technical systems. It is possible to find old data and plant designs that use other systems. It is not uncommon, in professional life, to find a problem in which units need to be transformed. This article aims to help people who have to solve this kind of difficulty, by giving an overview of the different unit systems. A description of traditional and unusual units is also included in this article. Undoubtedly, the best help will be found in the program included in a floppy disk(1). A software, in the Windows environment will enable whoever wants to solve, its units conversion problem accurately. The conversion technique, based on dimensional analysis, is used in the program and explained in this article.