The basic Calculator app that comes with iOS is good for simple calculations, and if you rotate your phone into landscape orientation, it even provides some rudimentary scientific-calculator functions. But if it's a full-featured scientific calculator you seek — or if you'd just like a great calculator for your iPad, which inexplicably doesn't include one — you'll want to look elsewhere.
My personal favorite remains TLA Systems's $10 PCalc (App Store link). It's overflowing with features, including scientific operations, conversions, constants, and even user-defined functions. And you get it all in an interface that can look as simple or complete, and as modern or retro, as you prefer.
(If you don't need all of the features of the full version of PCalc — or if you're not sure, so you don't want to spend $10 — you can instead pick up the free PCalc Lite, which offers all the basics of the full version, but lets you add some or all of the latter's features a la carte. The nice thing about this approach is that upgrading PCalc Lite with all of the available add-on packs — Conversion, Theme, Programmer, Engineer, Power User, and Multiple Line — costs the same $10 as buying the full version, so there's no risk in starting small.)
I reviewed the original PCalc for iPhone — the iPad didn't yet exist — way back in 2008, and I followed that with a review of PCalc 2 for iPhone and iPad in 2010. PCalc 3, which debuted last September and has since seen several updates, added a slew of new features and an iOS 7-friendly design.
As with the previous versions, you get all the standard scientific-calculator fare: inverse; roots; exponents; trigonometric functions; nested operations; decimal, hexadecimal, octal, and binary modes; RPN (Reverse Polish Notation — both HP and non-HP versions); and much more. There's still a time-stamped virtual tape for revisiting (and sharing) your calculations, as well as a register (called the stack in RPN mode) that displays memory contents and decimal-, hex-, octal-, and binary-base versions of the current number.
To make it easy to perform common calculations, PCalc provides preset conversions in a slew of categories: angles (for converting between six units of angular measurement), area (12 units), bytes (13), cooking (15), currency (33), density (6), energy (14), force (8), fuel efficiency (8), length (14), lighting (12), power (10), pressure (11), speed (11), temperature (5), time (9), torque (4), volume (17), and weight (10). For example, to convert meters to feet, you enter the number of meters, tap the Conversions button (labeled A>B), tap Length, and then tap Meters. You see a list of your measurement converted to every available unit of measure; tap Feet and the result is entered in the main display.
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