Hello
I am frequently confronted with this problem of rating on my plans. (see screenshots below). Is there a standard? Or are both types of quotes accepted and if so, I'd like to have your opinions. Especially on putting a = = manually!
Thank you in advance.
Cdt
Fred
Hello, it seems to me that the = = is not iso 9001 from memory
Hello;
It is true that with the advent of 3D tools, dimensioning is no longer what it used to be compared to our good old drawing tables...
Whatever your choice in the quotation, it is, in my opinion, essential to favor functionality and readability (while remaining consistent with current standards).
If you want to stay in a " personal " rating mode as your screenshots suggest, I would keep the odds =24= while prohibiting odds only with the ‹ = ›... Always ask yourself the question:
" Can I make this part if I only have the information contained in the drawing, without having the possibility of measuring..." »
Do the exercise with your second capture...=> What is the " length " dimension of your prism and where to perform the ø5mm drilling?
Kind regards.
Personally, I make the central axis protrude to signify symmetry, I find it clearer
Hello
It's mostly what tolerance applies since nothing is specified (even if we understand that it's the half value, the fact remains that this notation has been banned in ISO standards for a long time, even if I still see it in the mold but in general it goes with the age and habits of the captain)
Concerning the tolerance, when no tolerance is attached to the dimension, it is the general tolerance specified in the cartridge that applies (ISO 2768-mK/ISO 13920, ... for example)
Personally, I practice this kind of rating
This has the merit of being clear and it defines 2 reference surfaces if there were to be other operations to be dimensioned.
Already, on the first catch, the quotation is overabundant.
For the = =, for us, it depends on the customers. It seems to be related whether the manufacturing is done in-house or not.
Obviously, it is only used for secondary dimensions and it can allow you to catch a piece that is out of bounds overall but will have the right functionality (centered hole).
But as already said, it's not normalized but is it critical?
+1 for the quote represented by @Le_Bidule ... That said, I sometimes have to explain why some ratings are in parentheses (to our boilermakers but also to our engineers... (sic)... not to mention the ISO 2768-mK tolerance, do you learn this kind of thing more at school? 
).
and... Yes... @Cyril.f ... I am an old captain. 
Yes I know that ;), I'm talking about the = =
It all depends on the customer, as the old Captain said 
Everyone has their own standard, especially among the large industrial groups, since they are the ones who set the standards.
Personally, it doesn't bother me but I don't use it. I prefer to define planes or axes of symmetry or datum faces
Hello
So, if it's to be in line with the norm, you can forget about the ==.
This is a simplification, which everyone understands... but which has no legal value in case of a problem with a supplier in bad faith.
The "easiest" thing to do is to add a reference plane and then declare your dimension symmetrical with respect to this plane
Be careful @Maclane, I've already been told that the sides in parentheses are very strict dimensions that you have to keep XD
It seems to me that the dimensions in parentheses are only indications, not to be confused with the control dimensions surrounded by an oval bubble
You can remove the " it seems to me" 
