LOCUS lets you look at and analyze data from database tables. The tables consist of columns of parameters and rows of values for those parameters. The most common way to look at data with LOCUS is to plot one column vs another and to apply constraints to the data to be retrieved. For example, you might want to plot the plasma current vs the central temperature for only those plasmas that were heated with neutral beams. Furthermore, you may want to distinguish that data by the density of the plasma, which you do in LOCUS by specifying symbol contraints--data that fall into different density ranges are plotted with different symbols. You can look at and constrain on expressions as well as columns, allowing you to plot functions that involve columns from your tables like Te3/2. You can fit data, average it, integrate it, fit multiple parameters, and plot 3d data. LOCUS also has facilities for printing data, for creating and updating tables, and for executing arbitrary database commands.