# History and previous versions

## PCalc

Our first program (1993) replacing tables of probability distributions, was running on the command line under MS-DOS. It was written in Pascal by Sytse Knypstra and Arjen Merckens. In fact it was a combination of a calculator and a replacement of probability tables.

Download the compressed file PCalc.zip (50 kB), unzip it and start PCalc.exe under the program DOSBox.

## PQRS 2

Around the year 2000 PQRS (Probabilities, Quantiles and Random Samples) was designed as a tool for students using computer aided instruction of statistics in order to make printed tables obsolete. It had a graphical user interface. PQRS was written in Delphi and runs under Windows and - with the help of Wine - under Linux.

### Installation

Download the compressed file PQRS.zip (0.7 MB), unzip it and start PQRS.exe.

## PyQRS 3

In 2013 PQRS was rewritten in Python. In order to distinguish it from the previous PQRS version, and as a tribute to Python and its author, Guido van Rossem, the first letter in its name was replaced by 'Py'.

### Installation

PyQRS should run under Linux, Windows and MacOS if the following packages are installed:

• python2.7 (already included in many Linux distributions),
• python-pyside (for the graphical user interface)
• python-scipy (for the numerical computations) and
• matplotlib (for the graphics).

and

• numpy,
• dateutil,
• pytz
• pyparsing,
• six. Then download and unpack the compressed file PyQRS27.zip (22 kB) in a directory and in the same directory run:

python2.7 PyQRS.pyc or python2 PyQRS.pyc or python PyQRS.pyc depending on how python is known to your system.

## PyQRS 4.0

PyQRS 4.0 (March 2016) is functionally equivalent to its predecessor PyQRS 3. It runs on Android (mobile) devices.

The app is written in Python using the Kivy framework. This time we could not use Scipy as we did for PyQRS 3. The probability (density) functions and the cumulative distribution functions were therefore programmed in Python. The code could easily be adapted from the Delphi code we used earlier for PQRS 2.

## PyQRS 4.1

PyQRS 4.1 (June 2017) has an improved user interface over its predecessor PyQRS 4.0. It runs on Android (mobile) devices, and on the Linux (64 bits) and Windows (64 bits) platforms.

Screenshots can be found under USING PyQRS.