On 01:52 PM 7/03/2001 +1100, Geoff Harland said:
> > Using 2/3 of an inch or .67 of an inch, its obvious which one is the more
> > accurate. Maybe fractions rather than rounded decimals used in conversions
> > would allow better accuracy.
> >
> > Clive Broome
>
>In other words, rational numbers (i.e. the ratio of one integer to another).

Please express 0.5000000000 mm as a fraction of an inch (to better than 10 
significant figures).

This whole topic has gone on a little long.  I think some people need to go 
back to school and relearn the concept of significance. And others need to 
realise that the metric system does not claim to be exact, it simply a 
unified measurement system based on 10's - with the metre happening to be a 
little too long.  I note that Geoff Harland has taken the discussion onto 
the open forum - good move.

On real Protel matters, I think Geoff Harland is correct: I like the idea 
of changing the underlying base units within Protel to support exact 
conversion between imperial and metric.  Would require a new file format 
though - simply to just make the change in base units clear to the 
program.  Make for an interesting time if your PCB maker used a different 
base unit to you.  You could encode the base unit in the PCB file (this is 
what MicroStation does I think - maybe ACAD as well) but you would still 
need to ensure that only versions of Protel that understood the changeable 
base units could open the file.  Maybe one for the next version.

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