Plus42

Retro style scientific power with modern plotting and finance

Plus42 revives the classic HP-42S experience and pushes it into territory the original could only dream of. This is far more than a nostalgic calculator clone: it is a full scientific, financial, and graphing workbench for serious number crunchers.

At its core, Plus42 stays faithful to RPN (Reverse Polish Notation), making it instantly familiar to fans of vintage Hewlett-Packard calculators. Stack behavior, programmability, and numeric reliability feel precise and trustworthy, ideal for engineers, scientists, and calculators enthusiasts who demand reproducible results.

Where it really stands out is in everything it adds on top of that heritage. The expanded, resizable display with eight lines makes stack inspection and program editing far more comfortable than on classic devices. Algebraic expressions, reminiscent of the HP-27S and 17B/19B, let you mix RPN power with more conventional formula entry, which eases the transition for users not fully committed to stack-based thinking.

Attached units and unit conversions—modeled after the HP-48/49/50 series—turn Plus42 into a powerful tool for physics, engineering, and everyday conversions, reducing the risk of unit-related errors. Financial professionals will appreciate built-in time value of money functions and amortization schedules, which bring traditional business-calculator features into the same environment.

The two-dimensional plotting is a highlight: you can visualize functions, zoom and pan intuitively, and even find integrals and roots directly from points on the plot. This bridges the gap between a classic scientific calculator and a lightweight graphing tool.

The trade-off is a noticeable learning curve, especially if you are new to RPN, and the dense interface may feel intimidating at first. However, for power users and HP calculator veterans, Plus42 is one of the most complete and satisfying calculator experiences available today.