Unwanted rounding of dimensions

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GrahamKing
Posts: 9
Joined: Mon Jun 21, 2021 1:21 pm

Unwanted rounding of dimensions

Post by GrahamKing »

I'm a fairly new user, falling at the very first hurdle in the arch workbench. I cannot create a rectangle with the desired dimensions:

File, new, select arch workbench.
Select Top plane, using the orientation tool in top RH corner of workspace.
Create rectangle.
In properties, set position to [0 0 0]
In properties, set Height = 2435 mm and Length = 2725 mm.

The problem is that FreeCad changes these values to 2440.00 and 2730.00 mm respectively.

What am I doing wrong? (Apologies if this is a FAQ - I have searched for a long while, honest!)

I think I've eliminated snap-to-grid as a cause, but I might be wrong. Working plane is set to "auto".

OS: Ubuntu 18.04.5 LTS (KDE/plasma)
Word size of FreeCAD: 64-bit
Version: 0.20.
Build type: Release
Branch: unknown
Hash: 90735172918871eb9b19d6831a9a139775b7122f
Python version: 3.6.9
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.5.1
Locale: English/UnitedKingdom (en_GB)
openBrain
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Re: Unwanted rounding of dimensions

Post by openBrain »

Hi, Welcome,

Have a look at your 'Unit' preferences : https://wiki.freecadweb.org/Preferences_Editor#Units
GrahamKing
Posts: 9
Joined: Mon Jun 21, 2021 1:21 pm

Re: Unwanted rounding of dimensions

Post by GrahamKing »

Unit preferences are:
Unit system: Standard (mm/s/kg/degree)
Number of decimals: 2
Minimum fractional inch: 1/2" (greyed out)
openBrain
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Re: Unwanted rounding of dimensions

Post by openBrain »

GrahamKing wrote: Mon Jun 21, 2021 2:52 pm Unit preferences are:
Unit system: Standard (mm/s/kg/degree)
Number of decimals: 2
Minimum fractional inch: 1/2" (greyed out)
I think you have to increase 'Number of decimals' because internally FreeCAD applies this to meters as your numbers are greater than 1000 mm.
GrahamKing
Posts: 9
Joined: Mon Jun 21, 2021 1:21 pm

Re: Unwanted rounding of dimensions

Post by GrahamKing »

Thank you openBrain, that did the trick!

But how extremely counter-intuitive! The UI now shows 4 decimal places (2435.0000) as opposed to the previous 2 (2440.00), but what has really changed is the number of significant figures rather than the spurious decimal places. And the number of sig.fig. depends on the magnitude of the number, rather than the precision of the computer's arithmetic?? I see I shall have to be very careful indeed with this piece of software.
openBrain
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Re: Unwanted rounding of dimensions

Post by openBrain »

GrahamKing wrote: Mon Jun 21, 2021 3:10 pm But how extremely counter-intuitive! The UI now shows 4 decimal places (2435.0000) as opposed to the previous 2 (2440.00), but what has really changed is the number of significant figures rather than the spurious decimal places. And the number of sig.fig. depends on the magnitude of the number, rather than the precision of the computer's arithmetic?? I see I shall have to be very careful indeed with this piece of software.
Actually what I'm surprised is that numbers are displayed in mm...
Could you attach the file (or a minimal part) to show this ?
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bambuko
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Re: Unwanted rounding of dimensions

Post by bambuko »

GrahamKing wrote: Mon Jun 21, 2021 3:10 pm ...But how extremely counter-intuitive! ...
Yeah, it's counterintuitive in other direction as well:
https://forum.freecadweb.org/viewtopic.php?f=3&t=52057

Perhaps "my" setting will work for you as well?
I was equally surprised with FreeCAD logic :mrgreen:
I am using Link branch and Assembly3
you can also download ... and try it here
excellent Assembly3 tutorials here
GrahamKing
Posts: 9
Joined: Mon Jun 21, 2021 1:21 pm

Re: Unwanted rounding of dimensions

Post by GrahamKing »

Gladly.

Screenshot: Image

The FC file:
rounding_demo.FCStd
(3.9 KiB) Downloaded 26 times
Attachments
Screenshot_20210621_162914.png
Screenshot_20210621_162914.png (120.3 KiB) Viewed 1067 times
GrahamKing
Posts: 9
Joined: Mon Jun 21, 2021 1:21 pm

Re: Unwanted rounding of dimensions

Post by GrahamKing »

... and while folks are digesting that, I'd like to say thank you for the very rapid and helpful response. Meanwhile I'll let my bricklayer know that he doesn't need to bring his laser interferometer :)
GeneFC
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Re: Unwanted rounding of dimensions

Post by GeneFC »

openBrain wrote: Mon Jun 21, 2021 3:18 pm Actually what I'm surprised is that numbers are displayed in mm...
This sort of issue came up a couple of years ago. I don't have any references, but I recall that the behavior was workbench-dependent. The OP says he was using Arch WB.

I would have expected that all such considerations were built into the base application, but that may not be correct.

Gene
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