Oops, back to school I go. These two equations are effectively different. Regarding the manual, which is quite good as it is now, wouldn't you consider some kind of collaborative work? Luís On 21 August 2012 22:24, Sean Luke <[log in to unmask]> wrote: > On Aug 21, 2012, at 2:56 PM, Luís de Sousa wrote: > >> Nevertheless, I'd point that the expression: >> >> |(x − Xi )| + |(y − Yi )| ≤ dist >> >> actually defines a circle, not a diamond (this is obvious when dist >> is, say, larger than 5). > > Luis, the equation for a circle is: > > (x-Xi)^2 + (y-Yi)^2 <= dist^2 > > I believe the diamond equation is correct. >