The question remains: WHY switch back and forth? If the board is started in one unit, you are making it harder on yourself and others switching back and forth, even with NO round off errors. The grids are different, the trace widths are different (unless you LIKE typing two decimal places all the time). It is senseless to be switching it around, unless it is just to make extra work for yourself or your international partner. Why not just KEEP IT SIMPLE (K.I.S.S.) :) -- George Patrick Tektronix, Inc. Central Engineering, PCB Design Group P.O. Box 500, M/S 39-512 Beaverton, OR 97077-0001 Phone: 503-627-5272 Fax: 503-627-5587 <http://www.tektronix.com/> http://www.tektronix.com <http://www.pcb-designer.com/> http://www.pcb-designer.com It's my opinion, not Tektronix' -----Original Message----- From: icu-pcb-forum-bounce@xxxxxxxxxxxxx [mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Patrick Jabbaz Sent: Wednesday, August 24, 2005 14:58 To: icu-pcb-forum@xxxxxxxxxxxxx Subject: [PCB_FORUM] Re: Metric to English - English to Metric Here is the trick to make it work, In Allegro, You can switch units from metric to mils, and vise versa without errors, if you have the following setup: User Units mils use 2 decimal places User Units millimeter use 4 decimal places Using this process, allows you to switch back and forth without any round off errors. Patrick Jabbaz Sr. PCB Design Eng. Xilinx 2100 Logic Drive San Jose, Ca 95124 Direct: 408-879-4709 M: 408-621-6533 email: patrick.jabbaz@xxxxxxxxxx _____ From: icu-pcb-forum-bounce@xxxxxxxxxxxxx [mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Austin Franklin Sent: Wednesday, August 24, 2005 2:26 PM To: icu-pcb-forum@xxxxxxxxxxxxx Subject: [PCB_FORUM] Re: Metric to English - English to Metric Hi Richard, Perhaps more than a decade ago, the CPU and code speed may have been an issue. But, in the realm we are talking about (a printed circuit board and the range of numbers and precision necessary) IMO and IME the compiler imposes no significant restrictions, nor does the "math processor" in the CPU. Again, it is simply a matter of knowing where the decimal point is. In Allegro, you don't convert because the tool can not handle it. In a tool that can adequately handle it, this is not an issue. Regards, Austin -----Original Message----- From: icu-pcb-forum-bounce@xxxxxxxxxxxxx [mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of richard moffat Sent: Wednesday, August 24, 2005 5:15 PM To: icu-pcb-forum@xxxxxxxxxxxxx Subject: [PCB_FORUM] Re: Metric to English - English to Metric Cadence is probably making a compromise for speed. The way that other tools may allow a seemless interchange is to have a greater length of significant numbers in the internal database, especially converting metric->imperial. The programmers are restricted to that they are given: The C compiler, and the maths processor on the CPU. In short: don't convert! >>> austin@xxxxxxxxxxxx 25/08/2005 9:08:15 a.m. >>> Hi, > Conversely, 1/10 (0.1) cannot be exactly represented in base 2... I design ASICs, and I have done a LOT of arithmetic functions in ASICs, and use decimal points all the time. All hardware arithmetic functions are done in base 2. It's simply a matter of knowing where the decimal point is and using enough digits. Yet, it goes on to explain the solution (as I said, knowing where the decimal point is)...so I fail to see the *real* problem. As was pointed out, PADS has no problem switching back and forth between the two unit systems, so I simply don't believe Allegro can't do it as well. It seems like this may be a self imposed restriction: > The real issue is that some numbers can't be represented exactly in the > standard floating point representation. Why do they have to use "standard" floating point representation anyway? Sounds like someone programmed themselves into a corner, and instead fixing it, they are trying to come up with explanations...instead of solutions. Sigh. To me, this is a huge weakness of Allegro. Regards, Austin