This wall is off by 1/512"

Yep yep. This is why i keep my *high test* dims in the project, that go down to .000000001 accuracy, and then i tell people not to model by tracing other sources.

I have of course no clue about the imperial system, but when I put it all in millimeters (with 7 decimal places) and I calculate the dimensions manually (with my trusty calculator) they do add up to the overall dimension.

So all I can say is, this is weird !

In addition to Aaron's comment, I would recommend increasing unit precision generally. I had a project that the PM wanted dimensions shown at 1" precision. During construction, it came to the surface that the rounded values of a string of dimensions didn't total the overall dimension spanning the same distance. The result was that a depression in the slab and the framed walls around it didn't line up. There were many minimum clearances to maintain in that area, so several walls had to be removed and re-framed.

Yep. I’ve seen that before. Not a fan of 1” rounding.

Sounds like someone closed the dimensions in that bust. That’s bad form, especially with rounded dimensions. If the PM wanted dimensions rounded to the inch, the model should have been corrected so that the objects being noted were actually on an even dimension.

Jon

And how often can a building be drawn so no fractions are shown anywhere? 3/58" metal studs, 3 1/2" wood studs, and 5/8" gypsum board make that practically impossible. Granted, the design should be laid out with as course of precision as possible, but I don't think there's ever any reason not to display finer precision other than "fractions make my OCD hurt". I prefer 1/8" precision. If I'm losing 1/16" here or gaining one there, that's not going to hurt anything, and if the contractor wants to round that to the nearest 1/4" or 1/2", then that's fine so long they're maintaining required clearances.

It really will hurt stuff. People always *assume* 1/16" or 1/8" doesnt "hurt stuff," because they dont always think about the compounding of those "issues" across a building. And since its just a personal "decision," a lot of folks let that decision creep up, in tolerance. 1/16"? 1/8"? 1/4"? Not a good idea for people to be making those calls, when its not any harder or any more work to just model it accurately, and dimension it accurately.

Its not RELEVANT if the contractor can build to that tolerance or not. Its only relevant if someones way out of the discussion of "why isnt this built right" is to finger point.

1/16" rounding ended up with exterior walls of a building being 4.5 inches out of whack, on a building i just finished working on. Because not all items are parallel, and straight dimensions at one end of the building impact things on the other side.

AE firms need to get on board with modeling accurately, and dimensioning accurately, or finding themselves marginalized in Construction even more than they already are.

Modelling accuracy and construction tolerance are completely unrelated

Not entirely, if you round the model accuracy and then the construction is rounded from that you are compounding the error.