Kalk is an RPN calculator with a 30-level stack that performs the four basic operations, trigonometry and log functions. It offers a user-friendly experience with an easy-to-use interface.
One of the things I appreciated most about Kalk was its minimalist design. The calculator takes up very little screen real estate and requires just 40KB of disk space. Users are presented with either six or seventeen levels of the stack, depending on their preference. Additionally, the app features a useful quick-reference dialog accessible via the Help menu.
On the functionality side, Kalk offers a number of useful features including the ability to press Return or Enter to perform calculations, use the "=" key to swap values, and use Option-= or Delete to drop levels from the stack (note that Delete only works if the edit line is empty). The calculator also features a Pi approximation for trigonometric calculations, and the "E:" on the Edit Line changes to red boldface when there are fewer than five free levels on the stack.
The app also includes a few more advanced features, such as the ability to "program" Kalk by copying and pasting values separated by returns from a text editor or spreadsheet. Kalk's percentage function is also worth noting, allowing users to markup or markdown values much like the HP38E.
Some customization options are available as well. Users can change the background texture of the window using the "Desktop Patterns" Control Panel (System 7.5.0 to 7.6.1) as well as the app's beep sound by adding a System 7 sound file named "Kalk Beep" to their System suitcase.
Of course, like any piece of software, Kalk does have its limitations. It only runs on Mac OS Classic, so users with newer operating systems will not be able to use it.
Overall, I found Kalk to be a well-designed and functional RPN calculator that should be a welcome addition to any Mac user's collection.
Version 1.1.5: N/A