> Because it can eliminate having to manually transpose dimensions
> and therefore, a source of error.

Let keep it in perspective:  PCB design is governed by IPC ,  mechanical
widgets are govenened by ASTM, ASE,  ( not sure about  all  the acronyms)
but the whole point is IPC says  it must be viewed one way.   Not your way
or ASTM way etc.


> Sure. That makes perfect sense once it is complete. Does it define
> "primary side" ? Is that the side with the most bits, the one the
> through-hole parts are on, the one that matches all the mechanical
> drawings of the complete product or something else ?

Yes  IPC T50 defines the primary side as the side with the most components
sec 22.184

>
> I've never seen a drawing of a chair with the legs at the top, but I
> am sure it spends some time like that at the upholsterer. Why
> should it be any different when I am laying out a PCB ?
>
I cant speak for the chair  it is governed by "tag removal" laws which I do
not have documentioan on.  I guess the chair can be rotate without
contradicting IPC standards since IPC does not apply to the chair


> In fact, I have a job at the moment where it would be a really useful
> tool. There are two boards that plug together component side to
> component side. If such a tool existed, I could place components
> on both sides of a single outline so that I could check for
> interferences as I go. I could also put the connectors on top of
> each other so that I know they will match up. Once I am happy, I
> could select everything on the bottom layer and flip them with a
> copy of the outline. Now I have two boards as they will be
> manufactured on a panel, with the components on the top, no
> transposition errors and I still have the ability to keep in sync with
> the schematic.
>
You can flip x or y now  and it flips correctly  so why does anyone what to
flip so it contrary to design standards?  I dint get your point,  but I have
seen boards backwards  when these standards were ignored.  The problem is
that mech engineers and designer dont know how to view a board.


Mike Reagan
EDSI Frederick




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