> The equation would be x * (1/y) < x > x * y

This doesn't look like an equation to me, but I think I get what you want.=
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You are looking for a geometric progression with a known value at each end=
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of the scale and the geometric mean in the center.

> How would I (can I) resolve the equation to find 'x', the midpoint,
> if I have just the range, which in this case is 500kHz to 4100kHz ?

> I can guess at say 1400kHz. 1400/500 =3D 2.8. 2.8 * 1400 =3D 3920,
> which is close but there must be a better way

There sure is. Look at the following to compute the middle value:

SQRT(500*4100) =3D 1431.8

Now lets check that:

1431.8 / 500 =3D 2.8636

4100 / 1431.8 =3D 2.8636

So, we have found the correct 'middle' value.

Assume that the value we read from the pot (lets call it X) ranges from 0 t=
o=20
1, then we want:
        0 to map to 500,
        0.5 to map to 1431.8, and
        1 to map to 4100

The ugly function:

       500 * 2.8636^(X*2)

gives you what you want. Lets check it:

      500 * 2.8636^0 =3D 500 * 1 =3D 500
      500 * 2.8636^(0.5*2) =3D 500 * 2.8636 =3D 1431.8
      500 * 2.8636^(1*2) =3D 500 * 8.2000 =3D 4100.1

So, aside from a little rounding error we get the right answer.

-- Bob Ammerman
RAm  Systems
=20

--=20
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