Revit Dims and Accuracy

[david_peterson]

Today I was putting in a dimension string and notice something I didn't think was possible in Revit. And now I'm questioning how accurate Revit really is? Project uints and Dim type units set to 1/256" I place a dim string from col center to face of opening to face of opening to col center. I then placed a dim string from col center to col center (which resulted in a 45'-0" dim). The string that went to the openings didn't match the over string when you added them up. It was off by 1/256" So I adjusted the slab edge slightly to and set it to a real number. The only way I'm thinking the results I got are possible would be if I was somehow right in the middle of a 1/256".
So here's the question.
I believe with autocad, they run out precision to 14 decimal places regardless of what you have your units set to. I'm wondering if the same is true with Revit?
Anyone know?

[drdesignz]

I don't know, but I've also recently found a 1/256th of an inch difference in an overall dimension. I think I moved the last grid 1/512th of an inch to "fix" it.

[Scott D Davis]

The difference can come between "Project" settings and Dimension settings. Project Units can be set to be as accurate as 1/256, while Dimensions can have their own accuracy settings. Check under the Manage Tab, Project Units, then Accuracy to set the project Units. Then make a Dimension Type called "256" or something like that, and set the dimension units to use the project settings. Now both the project and dims will match the rounding, and you will see where the accuracy issues might be.

[twiceroadsfool]

Ive seen things off by less than 1/256", that causes dimensions to break. Most times i find the cause is:

1. As Scott mentioned, the Proj. units and dim units WERE different at some point (i dont know why, but when theyre different it seems more prone to modeling things OFF by less than 1/256")

2. Items were modeling by using the Pick Lines tool on a CAD plan. This is the more prevalent cause that ive seen.

As mentioned, you can offset/translate everything on one side of the dim by 1/512", and it corrects itself. But its annoying.

[djn]

I believe with autocad, they run out precision to 14 decimal places regardless of what you have your units set to. I'm wondering if the same is true with Revit?
Anyone know?

I have wondered the same thing, when Revit won't let me use the move tool to move an element less than a 1/32". I always get the dreaded "element too small on screen" error message.