> For the complete documentation index, see [llms.txt](https://swatplus.gitbook.io/io-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://swatplus.gitbook.io/io-docs/introduction-1/routing-units/untitled-2/frac.md).

# frac

The fraction of element in Routing Unit is a weighting factor. Each element’s hydrograph contribution is multiplied by an expansion factor derived from frac. For non-HRU objects, the expansion factor equals frac. For HRUs/HRU-LTEs with frac < 0.99999, the model converts frac into an area expansion factor by multiplying it with the Routing Unit area and then dividing it by the HRU/HRU-LTE area.

{% hint style="danger" %}
The model does not check the frac values. If they do not sum appropriately for a Routing Unit, the routed water/load scaling will reflect that directly.
{% endhint %}