Using Totals in Formulas in Revit Schedules

This has been a frequently asked question on the various forums over the years:
“Is it possible to use a grand total from a schedule in a formula in Revit”.  The first response is always No!  Then eventually someone will mention the arcane workaround but it is not always clearly explained so I have decided to show a simple example of what the problem is, and how the workaround might be applied.

I must confess that this is not my original idea – in fact I have found references to the workaround, as far back as 2006 on AUGI by Leonard Raiz (one of the Revit Founders).  More recently (2011), Martijn de Riet published a description of how to calculate a ratio between two area types – this includes the workaround but does a few extra tricks of calculating a ratio of two different sub-totals after first separating them from one grand total, so it is not that easy to understand just the ‘totals in formulas’ workaround.  Many thanks to Martijn, as I originally learnt the technique from…

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