However, there is a workaround for calculations involving site area. Enter the site area in project info. Then create an expression where you use string to number conversion because ArchiCAD does not treat site area in project info as number, but as text. Since the site area should not change, you should only have to enter it once.
You can do the same to compare zone areas to an overall building area.
Or for any element value that you want to compare to a 'master' value.
An alternative to using the project info (and having to convert to a numeric value) is to create a 'value' property with the master figure you want.
Then associate that property with the element type you are trying to calculate.
If you want to change the master figure you just change it in the Property Manager.
Unfortunately the master property can be changed in each element - it can't be locked - we have asked for this option.
If it is changed you will see the symbol changes to a custom value and it is easy to change it back to default.
I think this is a better option, especially when we can get Graphisoft to allow us to lock a property.
I don't think there will be too much danger in users changing the default in each zone (or other elements) though, so it should be fairly safe if unlocked.
When you are amending the 'master' value in the property manager, you will know if an element has been changed from default.
Remember, you can't lock the project info either.
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