Administration: Rules calculation

[Rom01]

With the rule "Set field value" you have three options:

1. set value with a fix value
2. copy value from (another) field
3. clear value

I miss the possibility to calculate a value.
For example calculate the sum of existing fields or calculate the difference of existing fields (Type date, integer)

[Spiegel]

This is a known limitation.

Placing it for votes