> For the complete documentation index, see [llms.txt](https://docs.videc.de/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.videc.de/acron-9.3/en/anlagenkonfiguration/verfahrensgroessen/autogroesse.md).

# Auto variable

Process variable determined automatically by way of an external variable.

The configuration of process variables defines how the various process values are handled by ACRON. So it is important to know the sequencing of the individual calculation steps involved in value handling.

Each calculation step is run through for all values of a day before the next step is carried out.

The bases of all calculations are the process values of the allocated external variables. This variable can also be a component element of a calculation formula. The result of this step is consequently either the actually process value or the result of the calculation on the basis of it.

In the next step, either the value handling or the value carried forward is applied to the result of the first step. If, for example, 'Difference from previous value' is selected as the value handling mode, the difference from the result and its predecessor is formed.

If the 'Carry forward process values until next change' option is enabled, the last valid result continues to be used until a new valid result is available from the first step.

If one of the available substitute value formation options is enabled, this final step is carried out. The substitute value is always formed on the basis of the result of the preceding step. So if the value of the difference fell short of or exceeded the preset limit value, the result of this step would be the corresponding substitute value.

Consequently, the displayed process values of a time frame can result from different step levels.

Process variables can be moved within the groups by [drag & drop](/acron-9.3/en/erklaerung_zur_bedienung.md#drag-drop).


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