The Slide Rule

by Marat Fayzullin

Nov 22 2008 News:
Minor update to Slide Rule for Maemo released. I have changed the keypad to look more like calculator instead of the phone dialpad. Also, the top row of N810 keys can now be used as digits without pressing the F-key.

What is it?

At the surface, the Slide Rule is just another calculator for your mobile phone. In addition to the usual arithmetic duties, Slide Rule can do much more though:

These features make Slide Rule more similar to the popular TI-8x machines from Texas Instruments than a generic run-off-the-mill calculator. In the future, I hope to add more features to the application, such as computing limits, numeric integrals and differentials, solving algebraic equations, and so forth.

The latest version of the Slide Rule can always be obtained from the home page. To get help, report bugs, suggest new features, and discuss Slide Rule and my other applications, use the discussion group at Google Groups. Now, let us look closely at how you install and use the Slide Rule.


[#] Slide Rule Maemo for Nokia N800/N810 tablets (or install directly to device)


The Slide Rule will run on any Nokia phone equipped with the 3rd Edition of the S60 software. It will not run on older S60 phones or UIQ phones from Sony Ericsson.

To install Slide Rule, download its .SIS file to your phone and open it. If installation fails, you may have to enable the phone to install applications from providers other than Nokia affiliates. To do this, go to Tools | Application Manager | Options | Settings and set "Software Installation" setting to "All".

Basic Operations

When you open Slide Rule application, it presents you with a screen shown above. The green area at the top displays the most recent computation results. It is similar to a paper roll in a printing calculator. The yellow area at the bottom serves to enter data. Just like in a traditional calculator, you type in arithmetic or algebraic expressions and get the answer by pressing the central button on the directional pad. If your phone is blessed with a QWERTY keyboard, it will work in the expected way. To enter data with the dialpad, use it as follows:

So, what happens when you click [ENTER] or the [OK] button? This depends on what you have just entered:

Arithmetic Operations

Upon clicking the [OK] button, the Slide Rule will try to evaluate any expression you enter numerically. This is possible when your expression does not contain any variables or all the variables can be reduced out of it. So, expressions like "1+13", "0.75/36+19", or "sin(0)*sqrt(x)" will result in immediate numeric answers. Any expression that cannot be evaluated to a numeric value, will only be simplified and treated as a function.

Unlike a traditional calculator, the Slide Rule attempts to keep integer and floating point portions of the answer separate, to avoid losing precision. While the floating point portions are treated in the usual manner, there are special rules when dealing with integers:

In order convert all integer portions, including ratios, to the floating point, press the [=] key or the [SOFT2],[OK] key sequence.

Algebraic Operations

Plotting Graphs

When in the calculator mode, you will see that some expressions are marked with colored letters  G . Press [SOFT1] to see graphs of these expressions in corresponding colors. While in the plotter mode, shown at the right, you can use the following keys:

Notice the red lines at the top and the bottom of the screen. These lines denote off-screen parts of the graphs.

© Copyright by Marat Fayzullin