Doug,

I doubt that this is even always possible.  Nomographs have been made in
a wide variety of forms.  Scaling on any one line might be linear,
logarithmic, trigonometric or "something else".  Identifying the form of
the scale may be nearly impossible, especially in the case of "something
else".

As an example of "something else", consider the Smith chart.  The Smith
chart is a very well defined example of a nomograph.  We know exacly, by
exact mathematical relationships, what is being presented on the chart.
  While this doesn't qualify as your "three lines" example, for certain
specific applications, under well defined limiting conditions, it would
be possible to unroll some of the information in a Smith chart into your
three line example.  Trying to determine, after the fact and without
reference to either the original chart or the underlying mathematics,
what scaling was used on one of those lines would be nearly impossible.

Best regards,

Dave


Doug Hewett wrote:
> Suppose a nomograph with three lines (A, B, and C) is scanned.
> What software package allows the user to select tickmark I on line A and draw a set of lines through tickmarks J on line B until they intersect line C?
>
> The software should interpolate the intersection on line C between the tickmarks.
>
> Accuracy of +/- 5% would be acceptable.
>
> Thanks,
>
> Doug Hewett, CSDP
>
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