ACCEPTED SOLUTION
Accepted Solutions
Let's instead use Ron's image from below:
All weak dims.
Let's say I change the 202.331 dim to be 300.000. This is what will happen:
- The left end is constrained to the reference and therefore won't move. So, the right hand vertical line will move to the right.
- The vertical line below it is tied to it so it will move right too.
- The length of that second vertical line is fixed (114.836) so it will not change.
- That will drag the bottom angled line to the right as well. It will not change angles because it is constrained as normal to the leftmost angled line.
- Because the bottom most horizontal line has a fixed length (74.649), it and the short vertical line at the left will move right as well.
- The far left bottom point is constrained to the reference and will not move.
I also know that if that vertical reference moves right or left, this entire sketch will move with it because there are no other vertical references.
Now, if I grab a line and drag it, Creo will allow the values of the weak dims to change. It also allows the values of string, non-locked dims to change, I believe, so no difference there.
All predictable because Creo tells me what till happen. Now the default scheme here creates a lot of cascading effects, but it's fully constrained and predictable.
If we sketched the same thing in SW all the lines would be lue and there would be no dims or constraints. I could grab and drag any line pretty freely and usually, only that line moves. What isn't clear, however, is what happens to the sketch if the rest of the part moves.
You mentioned below that Creo's weak dims and SW's blue sketches are the same. The above is why I say they are not. My point was not to critique SW (which I guess I did), but to answer the original question. The two sketchers do not behave the same, there are differences in methods that are important to understand if you are coming from one and want to bake robust designs in the other. There isn't really an equivalent of the "blue sketches" of SW, but I guess the image above is as close as it gets. It still provides a lot of info on how this sketch will behave, the default SW sketch provides almost nothing. Different ways of doing it and I strongly prefer Creo's.
In either tool you need to master it and put in the right inputs to get good results. Each tool, however, requires different inputs to get there.
Or because it's a terrible idea. 
I agree on the SW philosophy of making things simple and not giving the user info they don't think they need. But, I need to know how you are constraining my geometry. I hope Creo never implements anything like this. One of Creo's strength is the amount of info it gives you on the status and structure of your model.
Best I can tell, SW simply leaves the unconstrained sketch entities at the same location relative to the part origin as the model changes. But there's no real way to know, because SW doesn't tell you, and therefore no way to predict how your model will act.
My comments were on unconstrained sketches. You have no information on how SW handles those. I find no value in an unconstrained sketch in a parametric modeler, only uncertainty. That's what I was calling a terrible idea (somewhat, but not entirely, tongue-in-cheek 
) and one that I hope never finds a home in Creo.
As far as being able to predict how a Creo sketch made only with weak dims & constraints will behave, I can absolutely do that because I know that it's going to maintain this distance, these things horisontal, these things equal, etc. all relative to the references selected.
I didn't intend to open a SW vs. Creo debate, there are way too many of those already. I merely wanted to point out that all Creo sketches are fully defined by default, there's no such thing as an unconstrained sketch, like there is in SW.
Ok, we can agree to disagree about that terrible idea.
And as far as being able to predict how a weakly-constrained creo sketch will behave - this is what I had in mind when I asked the question:
Fully parametric; but can you really predict what will happen if this dimension is changed to be 40?
Let's instead use Ron's image from below:
All weak dims.
Let's say I change the 202.331 dim to be 300.000. This is what will happen:
- The left end is constrained to the reference and therefore won't move. So, the right hand vertical line will move to the right.
- The vertical line below it is tied to it so it will move right too.
- The length of that second vertical line is fixed (114.836) so it will not change.
- That will drag the bottom angled line to the right as well. It will not change angles because it is constrained as normal to the leftmost angled line.
- Because the bottom most horizontal line has a fixed length (74.649), it and the short vertical line at the left will move right as well.
- The far left bottom point is constrained to the reference and will not move.
I also know that if that vertical reference moves right or left, this entire sketch will move with it because there are no other vertical references.
Now, if I grab a line and drag it, Creo will allow the values of the weak dims to change. It also allows the values of string, non-locked dims to change, I believe, so no difference there.
All predictable because Creo tells me what till happen. Now the default scheme here creates a lot of cascading effects, but it's fully constrained and predictable.
If we sketched the same thing in SW all the lines would be lue and there would be no dims or constraints. I could grab and drag any line pretty freely and usually, only that line moves. What isn't clear, however, is what happens to the sketch if the rest of the part moves.
You mentioned below that Creo's weak dims and SW's blue sketches are the same. The above is why I say they are not. My point was not to critique SW (which I guess I did), but to answer the original question. The two sketchers do not behave the same, there are differences in methods that are important to understand if you are coming from one and want to bake robust designs in the other. There isn't really an equivalent of the "blue sketches" of SW, but I guess the image above is as close as it gets. It still provides a lot of info on how this sketch will behave, the default SW sketch provides almost nothing. Different ways of doing it and I strongly prefer Creo's.
In either tool you need to master it and put in the right inputs to get good results. Each tool, however, requires different inputs to get there.
I don't have access to Solidworks anymore, but signed up for free trial of Onshape; I'm pretty sure it uses similar technology (it's the same team, after all).
So far as sketcher is concerned so I can at least say that these are the rules you need to know about: if it's blue, it will stay in place*, and you can drag it around. If it's black it is constrained (and you can't drag it - this is actually where Creo sketcher is superior because of the extra control you have with the dimension lock/unlock)
* blue sketch will remain fixed relative to the part origin; for example, if the underlying solid is changed,:
Probably not what you want to happen, but it is not really unpredictable.
And so I agree with you about these tools being different and the requirements of understanding the principles of robust design.
However, for me, having auto-created dimensions does not provide much benefit - I still end up dimensioning the sketch according to my intent.
So for Creo, strategy is to "eliminate the red", and for Solidworks, it is to "eliminate the blue".
Ok, my rant continues 
In essence, I was objecting to the point of view that SW is inferior because it allows you to leave sketch geometry "unconstrained". Creo does the same thing by creating the "weak" dimensions and constraints.
So, I want to be on the record and state that I like the Creo sketcher. If you learn it, you can create robust designs.
But if you don't, then the poor soul that needs to change your design in the future is in a world of hurt.
Creo allows new users to create models that will be very hard to maintain.
(I know that you can implement modelcheck to refuse models with sketches that contain "weak" dimensions).
So I like the Solidworks sketcher more than the Creo sketcher.
Solidworks gives you the blue/black coloring method that I think is just plain better. It is more intuitive to grasp.
User training is easier: you tell your users that if they see anything blue, then they should re-examine their sketch, and impose dimensions and constraints that remove the blue entities.
Suppose a brand new user adds a dimension to their sketch and a line turns from blue to black.
This is feedback that automatically leads the user on the path to the correct conclusion that "black = constrained" and "blue = free".
In the end, it still requires proper training and experience to appreciate that black is better.
PS:
Does anyone actually use the "entity lock" feature? To me, this is an example of resources taken away from fixing what is really broken in the software.
PPS:
The config.pro option sketcher_disp_weak_dimensions no is a major mistake that can lead to a company having their CAD database full of confusing designs. What on earth is the point of this option - it certainly does nothing to ensure design intent?
You shouldn't
But if you insist, it is:
File->Options->Configuration Editor->Add->Type in "sketcher_disp_weak_dimensions" for option name; change value to "no"->OK
Paul, I seems as you have something set up differently than me. I get info just like you do in SW. When I first sketch everything comes up with blue dimensions like this.
I then can modify any dimension when I do they turn yellow like this. Or if I put in other dimensions it would get rid of some blue ones that are no longer needed.
I rarely use LOCK. 2-3 times per year. That would only be for some dimension I could never change for any reason. Some of my coworkers use at least one or two locks per sketch they use it as an aide in sketcher because they were taught to click and drag. Which can cause other dimensions to change also. So in short this is identical to the SW sketcher only using Blue and yellow instead of blue and black.
On a side note. Back in the day every Pro/E user had to become experts at dimensioning sketches. Your dimensions and constraints back in the day had to all be inserted manually and they had to mathematically work or you could not exit sketcher. So you learned how to exaggerate a sketch just so you could put the dimensions in how you wanted then tweak everything so it was the size you desired. I still instinctively use this same exaggerated sketch method today only now sometimes I can leave some blue dimension if it does not mess with my design intent.
