Significant digits.

[ian1196]

I use AutoCAD 2017 everyday. I am also learning Fusion360. Sometimes I generate a 2D drawing in 360 and save it as dwg. In AutoCAD, I open it and Exportlayout so I can use it to make measurements.

By default, it gives the results in 1 or two significant digits. I now have to cut and paste the drawing in another file because Precision only changes the values selected and if you make more measurements the door is open for mistakes.

How do I change the default parameters to 4 digits with trailing zeros? I want to change it once and forever.

Also, how does one change the same default parameters in Fusion360? Once and forever.

[Alfred.NESWADBA]

Hi,

>> By default, it gives the results in 1 or two significant digits

Please take care ... the number of displayed digits in dimensions depend on dimension style, the number of digits shown in the property window depend on the setting of precision in command _UNITS.

But all calculations done internally (like finding an intersection point) are done with full precision, independent of any setting.

- alfred -

[ryan.bales]

I can speak for Fusion here, In Fusion there are two places you want to do this - one is the preferences and the other is the dimension precision in drawings. You'll want to set general precision in preferences to make sure your models are drawn at the required precision. 

[Kent1Cooper]

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@ian1196 wrote:

....How do I change the default parameters to 4 digits with trailing zeros? ....

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If that question is about the text content of Dimensions, it's the DIMZIN System Variable that controls whether trailing zeros are included.  [It also affects the returned string from an AutoLisp (rtos) function.]

[leeminardi]

Be careful not to confuse significant digits  with decimal places. AutoCAD maintains about 15 significant digits no matter the location of an object.  As points, line ends, circle centers, etc. move away from 0,0,0 the number of decimal places in the database reduces such that a coordinate of one million would lose about 7 of the 15 decimal places it would have if were located within 1 unit of 0,0,0.  The lunits command sets the displayed number of decimal places.

[ian1196]

I used the term significant digits because it is what me the user uses to measure a physical part after manufacturing.

I understand that CAD software needs to uses enough digits so cumulative errors are not a problem.

I can open a file and spend a few minutes getting the display to meet my needs.

In both AutoCAD and FU360, I would like to make this change once and not every time I open a file. When I create a drawing from scratch, it keeps the display to my preference.

[leeminardi]

I interpreted your question as referring to the number of digits to the right of the decimal point.  The correct term is decimal places for that number.  Significant digits (a.k.a significant figures) applies to the sum of the number of digits to the left and right of the decimal point.  

[Kent1Cooper]

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@ian1196 wrote:

....

I can open a file and spend a few minutes getting the display to meet my needs.

.... I would like to make this change once and not every time I open a file. .... 

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Unfortunately, the System Variables that affect this are saved separately in each drawing, so with any drawings already existing that don't meet your needs, the "few minutes" [or equivalent below]  will be necessary, but it can be automated.  Your best bet is to have an acaddoc.lsp file, in which you include these lines:

(setvar 'luprec 4)

(setvar 'dimzin *)

(setvar 'dimazin **)

The first one is for the displayed-value precision.  The others are about the trailing zeros in Dimension text content.

* Use a value of 4 or lower

** Use a value of 0 or 1

Read about those System Variables to pick the values that suit your needs.

That will do those settings for you automatically  every time you open a drawing, saving you those "few minutes."  Put the same values in all your drawing template  files, and all new drawings will have the right settings.

You should probably also do an appropriate setting of the AUPREC value [read about it to pick the right one].

[ian1196]

Significant digits is correct. I click on two points and I get .31" . I now have to expand it to see if it is .3125. In this case, significant figures and decimal places are the same. I never designed parts that are 12300" long. Either terminology you use, it is important to show the anticipated accuracy.

For example, I carried a a 2d drawing of a flange from Fusion to Autocad drawn in inches. In the process, it carried over a format.  I measured a diameter and I got "3".  That would mean a value of 2-4" would be good significant digit wise. The intended diameter was 2.997" as it needed to fit into a 3.000" hole.

[leeminardi]

The intended dimensions of 2.997 and 3.000 both show 4 significant figures and 3 decimal places of precision.  It is true that 0.3125 notes 4 significant figures and also 4 decimal places of precision.  But change the dimension to 1.3125 and you have increased the precision to 5 significant figures yet still only have 4 decimal places. Be careful with “…accuracy” which is much different than precision.  Accuracy is a measure of truthfulness whereas precision is a measure of detail.  Arrows shot at a target that cluster close together but not near the bullseye have good precision but poor accuracy.