Re: gEDA-user: pcb crooked traces

[Armin Faltl <armin.faltl@xxxxxx>]

Gabriel Paubert wrote:
> Really, the inch is by definition 2540µm, not the other 
> way around since over 50 years ago.
>   
As far as I know, 1" = 25400um, but I see your point ;-)

The only practical consideration I see is, that the internal unit of PCB
allows handling with integer-arithmetic (makes comparisons a lot
faster and safer than floating point).
Assuming 32-bit signed numbers with 1/100mil this gives:
   254nm resolution and +-545.46m coordinate range
32-bit signed and 1nm gives:
   1nm resolution ;-) and +-2.147m coordinate range

I don't know, if pcb really uses fix-point arithmetics, but even if
not a reasonable internal unit has some importance. AFAIK with
floating point, the average internal number should be around 1.

HTH, Armin


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