Easy to get started and use for simple tasks, yet powerful enough for more advanced problems. Choose your display: normal, scientific, engineering, or accounting. Don’t like algebraic entry? Okay, they’ve got RPN for you, as well. Has a tape feature, so you can check the accuracy of your entries. No more adding a column of numbers multiple times, trying to get a consistent result. About the only notable thing I haven’t found yet is a graphing function, but that may just be me. This program is pretty deep, while still having a “shallow end” for newbies. Need conversions? PCalc has them for 19 categories of measurement: angle, area, bytes, cooking, currency, density, energy, force, fuel efficiency, length, lighting, power, pressure, speed, temperature, time, torque, volume, and weight. I threw away my separate units conversion program; it was harder to use and handled fewer conversions. Need built-in constants? They’re available in seven categories: astronomical, atomic, electromagnetic, mathematical, physiochemical, universal, and user-defined. Built-in functions in six categories, including user-defined. Also, PCalc has a corresponding iOS version, so you can have it on your desktop and on the go. I already thought it was just about perfect, but TLA Systems (the authors) seem to keep finding ways of making more improvements. Highly configurable. Highly accurate. Highly recommended. Sorry to gush, but I just think it’s that good.