Three ingredients are required to understand this program. First and foremost, familiarity with complex arithmetic is required. Given that the design is accomplished by using REC, an understanding of that language is evidently required, even though REC is mostly used for executing formulas on a pushdown stack using reversed Polish notation. Finally, the program is implemented in Objective C running under the NeXTSTEP operating system, to take advantage of its excellent visual interface and other attractive features.