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leeminardi
en respuesta a: CHAY.HOBSON

In my opinion, the way AutoCAD deals with units is at best awkward.  First off, the word “units” is misused in AutoCAD.  Here’s a definition of units:

   a quantity chosen as a standard in terms of which other quantities may be expressed.

Angstroms, millimeters, inches, feet, meters, smoots, kilometers, miles, and parsecs are all examples of units for length or distance.  The words from the UNITS command including  “decimal”, “architectural” and “engineering” are examples of formats for representing a number.  AutoCAD occasionally refers to these as Length Type.

As many have noted, AutoCAD is dimensionless.  When you create something at a coordinate of say 1.23, its location is in AutoCAD units.  You, the user, may be assuming that 1.23 represents inches but someone else may be assuming centimeters when they enter a coordinate of 1.23. 

The UNITS command does not set which units are being used.  There is no way in AutoCAD to set units! Reading the fine print in the Drawing Units dialog box it says “Units to scale inserted content.”

leeminardi_0-1665683469740.png

 

The UNITS commands sets the scale factor that will be applied when inserting a drawing into the current drawing.  It does not “set units”. If you assumed that inches were the units you were working with and the creator of the drawing you are inserting assumed centimeters then by specifying centimeters with the UNITS command prior to inserting the drawing it will automatically be scaled 2.54 upon insertion.

The units scenario gets even more interesting when it comes to plotting the drawing.  The paper size specified will affect the scale of the plot!  For example, suppose we have a drawing with a circle of diameter 12 (AutoCAD units) and within it a square of 6 units per side.  With the paper size set to ANSI A (8.5 in. x 11.5 in.) as follows:

leeminardi_1-1665683510421.png

The plot would look like this:

leeminardi_2-1665683543795.png

 

Relative to the 8.5 x 11 inch paper the 6 inch square looks the correct size.

However, changing the paper size to ISO A3 (420mm x 297mm or 16.535 in. x 11.69in) and plotting full size yields the following!

leeminardi_3-1665683592819.pngleeminardi_4-1665683632399.png

AutoCAD assumed that since you are using a metric sized paper then you must have assumed the metric units of mm when creating the drawing!  This is done even though AutoCAD does not store the assumed units with a drawing. The plotted drawing is thus scaled down by 25.4 and instead of a 6 inch square you get a 6/25.4, or 0.236… inch square on your A3 piece of paper.

 

Bottom line.  If you want to assume you will be entering values in inches then go ahead.   Changing the units style to architectural will show a distance of 18.0 as 1’ 6”.   For your drawing that is showing (as I understand it) 20.32 instead of 0.8 just scale the entire drawing by 25.4  ( 25.4 mm = 1 inch) about a base point of 0,0,0.

lee.minardi