Solar eclipse magnitude

I wrote a program to calculate the parameters of an eclipse.

For the 2006 Mar 29 solar eclipse I get the magnitude 1.0260, while he
http://sunearth.gsfc.nasa.gov/eclips...Mar29-Fig2.GIF
there is 1.0515.

In that site
http://sunearth.gsfc.nasa.gov/eclips.../SEcatkey.html
it is said that: "Eclipse magnitude is the fraction of the Sun's diameter
obscured by the Moon."
which is clearly wrong because with that definition the maximum magnitude
would be 1.

In my program I used the formula:
G= (Sl + Ss - d) / 2 / Ss
where Sl and Ss are the Moon and Sun semidiameters and d is the distance
between the center of the Sun and of the Moon.

With my prog I get the NASA's magnitude when I do Sl/Ss which is 1,0521.

Is there any standard definition for the magnitude?

Thanks
Cristiano