Documentation for PLCalc, and downloading options for a standalone version, appear below the applet.

Here are the options:

• PLCalc can be run directly from this page as an applet (above). Since PLCalc doesn't load or save any files, this is a reasonable way to use the program.
• The PLCalc Java JAR file can be downloaded and run locally: click to download (79KB).
• The GPL-licensed PLCalc source TAR archive can be downloaded and compiled locally: click here to download (82KB).

First, if the applet doesn't appear above, if all you see is a gray square, chances are your Java runtime engine is out-of-date or not present. To solve this problem, go to http://java.com and download the current version of Java.

I've written any number of computer-based calculators over the years, with varying degrees of success. As time passes, as I figure out what features they should have, they are gradually becoming more useful.

I had recently been thinking about writing yet another calculator when I got an e-mail from a civil engineer asking for a relatively exotic feature — he wanted a calculator that could accept and display numbers representing feet, inches and fractional inches — numbers that look like this: "9 feet 3 7/16 inches."

My first impulse was to tell this fellow to switch to Metric, which does away with such things, but on reflection I decided that wasn't realistic. This came to me the day NASA lost a $125 million Mars spacecraft because two teams got confused about which measurements to use — they sent commands to the spacecraft using the wrong measurement scheme, and the craft burned up instead of entering a Mars orbit. On realizing their mistake, these hotshot aerospace engineers more or less said, "Oh, well, we'll just have to try again."

All my calculators are RPN — that's Reverse Polish Notation — an efficient, parenthesis-free way to process equations. I have always preferred RPN calculators, especially back before there were personal computers and calculators were much more important than they are now, because RPN requires an absolute minimum of keystrokes to produce results.

When a computation is trivial, there isn't much difference in procedure between an algebraic and an RPN calculator:

17 + 23

Algebraic:

• Type 17
• Type +
• Type 23
• Type =

RPN:

• Type 17
• Type "Enter"
• Type 23
• Type +

But when calculations become complex, and in particular when the required operations are in a nonintuitive order, the advantages to RPN become obvious:

5 + ((1 + 2) * 4) - 3

Algebraic:

• Type 5
• Type +
• Type (
• Type (
• Type 1
• Type +
• Type 2
• Type )
• Type *
• Type 4
• Type )
• Type -
• Type 3
• Type =

That's 14 entries.

RPN:

• Type 5
• Type 1
• Type 2
• Type +
• Type 4
• Type *
• Type +
• Type 3
• Type -

That's 9 entries.

Another advantage to RPN is there is normally a stack on display containing your recent entries, so if you get confused during a long calculation, the stack display will help you stay focused. The stack contains your most recent entries in a last-in first-out scheme. Typically, when a mathematical operation is needed, one or two numbers are removed from the stack, the operation is carried out and the result is returned to the stack.

Unlike a handheld calculator, PLCalc's stack is not limited to four entries, indeed its stack size is for all practical purposes unlimited.

PLCalc has lots of useful features:

• RPN architecture, 16 decimal point resolution.
• Full set of scientific and engineering functions.
• Financial computations.
• Statistical computations.
• Number base conversion.
• Multiple input and display options including hour, minute and second, hour and decimal minute (such as is used in GPS positions), and feet, inches and fractional inches for those unfortunates still obliged to work in these units.
• PLCalc remembers recent entries and recalls them for you using the up and down arrow keys.

Again, PLCalc is released under the GPL, and is Copyright © 2009, P. Lutus.

• 02.26.2014 Version 2.4. Fixed an error in the displayed formatting of statistical results.
• 10.23.2009 Version 2.3. Replaced string-based keyboard identifiers with keycodes for the benefit of non-English users.
• 08.30.2009 Version 2.2. Adopted a more robust strategy to detect the keyboard "Backspace" key in the base converter module.
• 08.25.2009 Version 2.1. Fixed a keyboard internationalization issue having to do with entry deletion in the base converter.
• 08.25.2009 Version 2.0. Corrected some minor cosmetic errors.
• 04.18.2009 Version 1.9. Fixed some locale-dependent numeric formatting issues.
• 04.17.2009 Version 1.8. Improved unit converter formatting and appearance.
• 03.31.2009 Version 1.7. Recoded to pay attention to numeric locale issues. There are circumstances where Java will ignore the current locale when printing numbers, but at least this program will now accurately honor locale when reading numbers. Also recoded the conversion utility for simpler operation.
• 03.28.2009 Version 1.6. Simplified the code base by eliminating the Java Web Start option.
• 03.04.2009 Version 1.5. Dropped the other shoe and added cubic yards to volume units in conversion database.
• 03.04.2009 Version 1.4. Added cubic millimeters to volume units in conversion database.
• 03.01.2009 Version 1.3. Added unit conversion utility.
• 02.08.2009 Version 1.2. Changed granularity in foot-inch-fraction display to 1/32 inch, fixed a number entry bug.
• 02.07.2009 Version 1.1. Corrected a display rounding error.
• 02.07.2009 Version 1.0. Initial Public Release.