Creating an analytical tool which is both efficient and flexible can be a difficult task. Many decisions must be made along the way to satisfy the end user as well as the developer. Although the user is very concerned about the system interface and form of the output, the internal program structure is of little interest. The developer, on the other hand, must produce an efficient software package that is easily modified to adjust to the needs of diverse users. Some of the important considerations that went into the initial design of LUCAS are discussed in the following sections.