Constraint in the slot - where is it coming from?

[MauiWarrior]

Hi All,

I am following this tutorial: https://wiki.freecadweb.org/Toothbrush_Head_Stand. I am at the part

Make the centers of the second slot coincident with the centers of the first slot with Constraint PointOnPoint.svg Coincident.

I was able to make the left two centers coincide, but when I select two right centers and try to add coincident constraint, I get error message: "Sketch contains redundant constraints. Please remover the following redundant constraint: 14."
It looks like constraint 14 is on length of the slot, where did this constraint come from, I did not set anything. Overall is it possible to get more details on the constraints? For example, I am not really sure what constraint 14 is, I am only guessing.

I attached the file with sketch.


Detail:

OS: Windows 10 Version 1809
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.24276 (Git)
Build type: Release
Branch: releases/FreeCAD-0-19
Hash: a88db11e0a908f6e38f92bfc5187b13ebe470438
Python version: 3.8.6+
Qt version: 5.15.1
Coin version: 4.0.1
OCC version: 7.5.0
Locale: English/United States (en_US)

[wieszak17]

It must be a bit old tutorial. Currently FreeCAD is more strict when comes to redundancy. Problem here is that coincident constraint on second pair limits two things: distance between left and right center (which is good) and radius of that arc (which is already determined so it is bad). You should select one horizontal line from first slot and one from second slot and make them same length.

Also FC reports all/first/any involved constraints when there is redundancy, sometimes this is confusing. Usually last added is a problem.

[MauiWarrior]

Thank you so much, it makes lots of sense.

[Kunda1]

Anyone feel like modernizing the tutorial?

[MauiWarrior]

This is off topic, but this tutorial uses both mm and cm. Should it be all expressed in one unit of measurement?