Forums >> Revit Building >> Technical Support >> Dimension String Doesn't Equal Overall Dimension

salarch2

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Joined: Fri, Dec 2, 2005
21 Posts

I've searched this problem but didn't seem to find a solution.  I have run into a big problem with dimensions in Revit that I hope is just something I'm missing.  I am using Revit 2009.  When I run a string of dimensions across a building, it doesn't always add up to the Dimension shown on the total dimension Length.  When it is off, It is generally off by whatever the dimension threshold is set for.  1" threashold when it is off is usually off 1".  1/8" off 1/8".

 I know it has to do with the rounding off in Revit but I would think the program should be able to determine the correct total.  It may not sound like a big deal but it is a big deal when the contractor adds it up and tells you there is a discrepancy.

Please let me know how anyone has resolved this problem.

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rkitect

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Joined: Thu, Dec 16, 2004
792 Posts

The resolution here is to be sure you have your tolerances set to 1/256 and have everything dimensions to the exact dimension they should be.  Somewhere something has been moved by just enough of a fraction to make Revit have to round, and it usually rounds in the wrong direction, unfortunately.  I have only seen one instance where setting the tolerances to 1/256" and haveing everything dimensioned exactly as it should did not work and that was a calculation error on the engineers part (yes, they aren't as perfect as they think they are Xp).

My recommendation for you is to make your dimension type have a tolerance of 1/256" and see where the nudge has happened.  Fix that and your dimension will read correctly.

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salarch2

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Joined: Fri, Dec 2, 2005
21 Posts

Thanks.  I know the problem happens because some are rounded up and some are rounded down.  Are you suggesting keeping the tolerance set to 1/256.  That would give you some pretty "ugly" dimension numbers.  We generally use 1/8" tolerance.

Anyone else come across this problem? 

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lunchtrayrider

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Joined: Sun, Jun 24, 2007
592 Posts

Honestly the best way to solve this problem is to just draw exactly what it is supposed to be and not accept any sort of wrong dimensions. Lots of times this is caused by putting in a wall, dimensioning to it, and then using the move command based on what the dimension says (and since your using 1/8" tolerance it could be off). the best practice method is to type in the temporary dimensions to set the wall at exactly what it is supposed to be. Also, a couple of easy ways to check dimensions is to click on what the dimension is dimensioning so it turns into a temporary dimension. then click on the blue text of the dimension and see if it is giving you a crazy fraction. if it does, correct it. the other way to check is to simply click on the dimension so that it is selected. then go to the element properties dialog box. for dimensions you'll notice that there is a field called value. it is grayed out so you can't change it here but you can see what the true unrounded value of the dimension is.

semi-edited for bad grammer, horrible typing, and other general lazyness. 

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RLAKES

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Joined: Thu, Jun 14, 2007
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Attached is an example of how the error accumulates (the same thing could be done to show how 1/8" rounding can go wrong).  The reason this has piqued my interest is that I heard that AutoCAD has to ability to round the dimensions within a single string in an alternating way so that the overall ends up the same as the sum of the smaller stringed dimensions. 

Instead of always rounding up, I'd be nice if it also rounds down sometimes to balance out the total.

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