Inconsistent Units ! Probably THE error box in Revit that have caused me the most grief, over the years I´ve spent hours and hours on trying to work around it. But once I got the hang of it, and not least once I understood WHY Revit would throw that error box at me, it´s not that bad. Hope some of you will find this helpful.
Let´s begin with some basic algebra:
<100 mm * 100 mm = 10,000 mm²>
So if you have a Length parameter, and try to use a (Length * Length) formula, you´ll get the " Inconsistent Units" error, because (Length * Length = Length Squared). Only way around is to neutralize the units on at least one of the parameters in the formula. The easiest way to neutralize a unit is by dividing by 1 (one):
<100 mm * (100 mm / 1 mm) = 10,000 mm>
Why? Because <100 mm / 1 mm = 100> (unit less) and <100 mm * 100 = 10,000 mm>
And another example:
<100 mm * 100 mm * 100 mm = 1,000,000 mm³>
So again, if you need to multiply 3 length units in a Area or Length parameter, you´ll need to neutralize the units as above.
<100 mm * 100 mm * (100 mm / 1) = 1,000,000 mm²>
<100 mm * (100 mm / 1) * (100 mm / 1) = 1,000,000 mm>
So far, dividing by 1 (one) have been a success, but in some cases it´s necessary to multiply by 1 (one) instead. An example: You want to multiply two Number parameters into a Length parameter:
<100.0 * (100.0 * 1) = 10,000 mm>
Another common situation for the "Inconsistent Units" error, is when quantifying costs in schedules
In the schedule you already have "Area" and "Cost" but want to add a Calculated Value "Total Cost":
<Area * Cost = Inconsistent Units>
<(Area / 1) * Cost = Total Cost>
There´s probably a gazillion other possibilities, but I hope that this explains why we are getting the Inconsistent Units Error, and how to work around it.