Enter — RPN Calculator

Enter is a Reverse Polish Notation calculator with a true four-level stack — for people who think in RPN and are tired of hunting for the equals key. Free to download, with every everyday function included. There are no parentheses and there is no equals. Type a number, press ENTER, type another, press the operation. The answer is already there. A TRUE FOUR-LEVEL STACK X, Y, Z and T, with T replicating as the stack drops — so a constant stays where you put it and repeated operations simply work. LAST x brings back the argument the previous function consumed. Roll up, roll down, exchange X and Y. Ten numbered storage registers that survive a relaunch. THE FUNCTIONS • Arithmetic, powers, roots and reciprocals • Sine, cosine and tangent with their inverses, in degrees, radians or gradians • Hyperbolics and their inverses • Natural and common logarithms with their exponentials • Percent and percent change, integer and fractional parts, absolute value, modulo, factorial • Combinations and permutations, polar and rectangular coordinates, decimal hours to hours-minutes-seconds • Twelve significant digits, shown as FIX, SCI, ENG or ALL UNDO, AND A PAPER TAPE Fifty levels of undo and redo, covering the stack, the registers, and whatever you were part-way through typing. The paper tape prints every number and every function beside its result — tap any line to lift that value straight back onto the stack. It survives a relaunch and copies out as text. CONVERSIONS AND CONSTANTS Ten quantities — length, mass, temperature, volume, area, speed, pressure, energy, power and force — with exact factors wherever the definition is exact. Twenty physical and mathematical constants, searchable, carried at full precision rather than rounded to the display. ON THE MAC The whole keyboard: digits, operators, Return for ENTER, Escape to clear, letters for the functions. A menu bar carrying the stack operations and the display modes with their shortcuts. FREE, WITH ENTER PRO Free: the stack, arithmetic, square roots and squares, reciprocals, percentages, the ten storage registers, undo, and the rest of the everyday keys. Enter Pro, one purchase with no subscription, unlocks the scientific functions — trigonometry, logarithms, exponentials and powers — along with the paper tape, conversions, constants and the extended function list. It covers every iPhone and Mac on your Apple Account, and Family Sharing. Bought Enter before it was free? Everything stays unlocked. DESIGNED, NOT PORTED Keys that depress under your finger, and a keyboard of its own when you turn the iPhone on its side. Properly typeset notation — real superscripts, and a radical drawn to the weight of the type around it. A two-line display showing Y above X, so you always know what the stack is holding. PRIVATE No accounts. No analytics. No tracking. Nothing you calculate leaves your device.