Thursday, January 26, 2012

Revit Inconsistent Units

Whilst searching the forums trying to get my head around why Revit is always telling me I have inconsistent units in the calculated values in my schedules, I came across this little beauty on the Revit Forum

It really does hit the nail on the head, and is well worth printing out and keeping hold of, thanks to Klaus Munkholm for sharing this one!

....."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 / 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...."

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