Contractor has sent me DWG file set to wrong units, how to respond?

[Christiaan]

A contractor has sent me a DWG file which reports its model space units as being mm. But they're not. To import the file at the correct scale I have to use custom model space units of 1 to 71. (they've drawn their drawing at 1:71 scale, so where that comes from.)

What should I tell them they need to change to correct their file so it doesn't incorrectly report the file units as mm? Or even better: so it imports correctly when set to mm.

[zoomer]

1:71, very interesting.

So you don't get their CAD geometry but their plan output,

like VW viewports.

As 1:71 seems a little strange and I never heard that before, I would even

think that it is possible that they may not draw CAD in 1:1 but in that scale.

I think the easiest way would be to save a custom Import Setting with

that 71 factor.

[Art V]

Making a bit of a guess here...

The 1:71 scale is interesting and I'll give some train of thought that may be of some help in case it does apply.

Paper size in the A-format range has a square root of 2 ratio (i.e. factor 1.4xxx).

The inverse of this is 0.707xxxx i.e. approx. 0.71

If scaled by a factor of 100 you get 71

It could be that the drawing has been scaled in model space to fit a paper size that is one size different than the size for which it has been drawn at a certain scale.

E.g. if drawn 1:100 at A1 it would be approx. 1:71 at A0 after scaling it up to fit A0 output size.

I don't know if this is the case, and it would be bad workflow to scale a drawing like this for paper output size but I have seen stranger things over the past 20+ years.

[Art V]

Oh, and to answer your question on what to tell them... ask them what units and scale (in those units) their drawing is using.

That is probably the best way to sort this out.

Units and scale are independent, it only matters if you select the wrong unit upon import at a certain scale that may give you a 1:71 scale in another unit.

Given that, I can't think of a unit combination right away that would give this ratio based on just units so it is either a rare combination of scale in a certain unit that gives 1:71 in millimetres or it is perhaps what I wrote above.