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From: R_Tim_Coslet@cup.portal.com
Newsgroups: comp.lang.ada
Subject: Re: Types with physical dimension
Message-ID: <123813@cup.portal.com>
Date: Thu, 29 Sep 94 19:06:39 PDT
Organization: The Portal System (TM)
References: <GRAHAM.94Sep27181841@canopus.clsi.COM>
  <36bss8$79@gnat.cs.nyu.edu>
Date: 1994-09-29T19:06:39-07:00
List-Id: <comp.lang.ada>

>"What do Ada programmers do to guard against dimensional errors"
>
>Probably not much, because in practice, at least in my experience, such
>errors are rare, although they are an obvious target for theoretical
>discussions.

When is 0 multiplied by 0 equal to 4 million?

When a programmer dropped an equation from a data sheet directly
into the code, without thinking that the equation used units of volts
but the A/D converter supplying the numbers has some "arbitrary"
unit scaling and is offset binary instead of twos complement.

Example:

	0V = 2048 A/D converter units.

Therfore 0V * 0V = about 4 million.


Admitedly not directly related to the current subject, but does
illustrate a case of a problem with processing real world physical
data without thinking the units and scaling thru...

At least Ada reported constraint errors instead of just scrambling the
result and giving a totally inexplicable wrong answer like Certain
other languages would :-)

                                        R. Tim Coslet

Usenet: R_Tim_Coslet@cup.portal.com
        technology, n.  domesticated natural phenomena