kicad-developers team mailing list archive

[Lorenzo Marcantonio <l.marcantonio@xxxxxxxxxxxx>]

On Mon, Oct 22, 2012 at 12:44:47PM +0200, László Monda wrote:
> As absurd as it might seem only picometres would be small enough to
> provide the needed resolution to not loose accuracy.

The nanometer was chosen to fit the 32 bit integer, avoiding heavy fp
stuff. Also fp has even greater rounding issues...

The other consideration is that everyone in the industry is going metric
(even traditional imperial pitches are often rounded to 0,05 mm). The
change was not only to have greater resolution but (IMHO especially) to
represent *exactly* decimal sizes (a 0,3mm hole is not exact in
decimils, for example)

The real question is: what do you use for a 1/16 decimil resolution
board? in fact there would be issues generating a gerber with that kind
of decimal figures... you're entering the GDS II format realm (i.e.
photolitho stuff)

> PS: By the way, just for historical reasons what was the resolution of
> KiCad before the nanometre era?

1/10 mil was the internal pcbnew unit. 1 mil is still the internal
eeschema unit. And it's not so historical since the default is still
a decimil build.

-- 
Lorenzo Marcantonio
Logos Srl

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