# Options

PK-Sim® can be customized using several options. To do this click on the **Options**

Button ![](https://2377851789-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LNl6UIiFP7k0sNQthlR%2F-M58ZieyU8EXF0Gy0fyh%2F-M58ZkhHjF4Is1uOACTS%2FSettings.ico?generation=1587151082445256\&alt=media) within the **Utilities** Ribbon Tab.

Within the **User** Tab, you can specify the following user specific options:

## Numerical Properties

* Allows scientific notation: You can specify if parameter values and results are displayed in scientific notation and if they are very small or very large.
* Decimal place: You can specify the number of decimal places displayed for parameter values and results.
* Maximum number of processors to use
* Absolute tolerance and Relative tolerance: You can specify the absolute and relative tolerance in order to control the error of the ODE solver. Changes will only effect simulations that are created after changing values.

{% hint style="warning" %}
Setting tolerances lower than default values (absolute tolerance: 1.0E-10; relative tolerance: 1.0E-5) may cause conversion errors in simulations following oral administration.
{% endhint %}

## Look and Feel

* Active skin: By changing the skin in the Skins group next to the Options icon the graphical appearance of the program can be changed.
* Number of recent file items shown: Changes the number of recent documents displayed within the File Tab. The program needs to be restarted for the changes to take effect.
* Preferred view layout: Choose from either tabbed or accordion view in e.g. the Compound window.
* Restore opened view when loading project: Open tabs (e.g. particular simulations, individuals or compounds) are saved upon saving and restored when re-opening the project.
* **Show software update notification if available**: When enabled and connected to the internet, a check for new versions of PK-Sim® is done automatically.

## Defaults

* Default species and Default population: Changes the default species and default population used for creation of a new individual.
* Default parameter layout: Changes the default parameter layout used for parameters shown within the Anatomy & Physiology tab of an individual and within the Parameters tab of a simulation.
* Lipophilicity, Fraction unbound and Solubility: You can specify the defaults for the description used for the Experiment input box when a new compound is created.
* Population analysis: After the first simulation run an analysis window opens automatically. The default type of this first analysis ('Time Profile', 'Box Whisker', ...) is set by this option.

## Icon Sizes

You can change the size of the icons displayed within the **Tree view**, the **Tabs** and the **Context menu**

## Template Database Path

You can change the path to the template database or create a new template database by clicking on ![](https://2377851789-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LNl6UIiFP7k0sNQthlR%2F-M44ssJgF6-4VQUDSwZe%2F-M44staEWJcox8k__Vmj%2FAddAction.ico?generation=1586015477060009\&alt=media)

## Colors

* Formula parameter: Changes the background color for parameters which are calculated by a formula.
* Parameter changed: Changes the background color for formula calculated parameters which have been manually changed by the user.
* Chart background and Chart diagram background: Changes the chart colors. For simulation charts, this is the default if no other color is specified in the Chart Editor of the Results Tab.
* Disabled: Changes the background color of all boxes with non-editable content.

Within the **Application** Tab, you can specify the path to a species-specific **Expression Database** you would like to use. To do so, click on the three dots in the **Expression Database** column in the row of the species you require.

![Linking a species-specific expression database to an individual.](https://2377851789-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LNl6UIiFP7k0sNQthlR%2F-LQJPSoNjgtDlxBl9HHq%2F-LOWQ4xemjDdWWTX5H9Y%2Fexpression-database-options.png?generation=1541162017238333\&alt=media)

The available expression databases can be downloaded from <http://setup.open-systems-pharmacology.org/>