Units play a major role on any simulation software. What are units? Which units are present in specific physics problems and the various types of units that exist for the same physics are a small list of this world. Some times units can be a big headache when we want to send data from one system to another. A good example where I have struggled with this was in combining Ansys with LS-Dyna; fortunately today interchanging k files is a breeze but this was not so in the past.