how to the other pcb cad programs handle this issue anyone know? Dennis Saputelli
Ian Middleton wrote: > > Here is how to measure a metre. > > http://www.npl.co.uk/about/history_length/page09.html > > "The metre was defined as "the length of the path travelled by light in a > vacuum during a time interval of 1/299 792 458 of a second" " > > The definition of an inch is derived from this. 1 inch = 0.0254 metres. Note > it was only during the 2nd world war that the Amrican Inch became equal to > the British inch. This was only found out when aircraft wings made in the US > had problems fitting to bodies made in the UK. Maybe protel are still using > the pre-war inch, which could account for the rounding errors ? (NOT) > > I agree the rounding errors in Protel PCB between metric and imperial are > really annoying, making things fall off grid. Many a time I have editted a > pad/part/track when I see 29.999999mm and think "Hey this should be 30mm" > and accidently go and edit it to 30.9999999mm. Grrrrrrrrrrrr. > > Ian > > > -----Original Message----- > > From: Ian Wilson [mailto:[EMAIL PROTECTED]] > > Sent: 02 August 2002 00:47 > > To: Protel EDA Forum > > Subject: Re: [PEDA] OT Metric vs Imperial > > > > > > On 12:08 PM 1/08/2002 -0400, vincent mail said: > > >John Ross wrote: > > > > > >>Metric or Imperial does not make any real difference (except individual > > >>preference) except when having to convert. > > >yep agree > > > > > >>I think the point is that Protel has never handled Metric properly due > > >>to, what I assume is shoddy conversion due to database limitations. > > >>Metric support in the SCH for rules definition was skipped altogether > > >>until DXP (NOT). > > >> > > >>Not all imperial values do work out to round numbers due to the > > generous > > >>tolerances that manufacturers apply to their values in data sheets. Try > > >>measuring a 20 mil (0.5mm) device and see! > > >>What is missed in the argument is that we will have rounding errors > > >>either way unless the s/w and/or database supports BOTH systems equally > > >>or not at all, and that includes the rules system. > > >well there isn't a real conversion to start with . most people say that > > >25.4 millimters equals an inch , that is if you round it yes. i seem to > > >recall the ral number has lake 5 or 6 digits behind the comma. and then > > >you get into floating point problems. > > > > > > 25.4 is exact by definition - hence the advantage in the base unit being > > some small fraction of a mm. > > http://lamar.colostate.edu/~hillger/everyday.htm > > > > Ian Wilson > ************************************************************************ * Tracking #: FFCC9E0F73BA494299F0241E4BAC8FEEE2220295 * ************************************************************************ -- ___________________________________________________________________________ www.integratedcontrolsinc.com Integrated Controls, Inc. tel: 415-647-0480 2851 21st Street fax: 415-647-3003 San Francisco, CA 94110 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/proteledaforum@techservinc.com * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
