Hello everybody
i need help with this:

with openscad 2018.06.14 from github

this code:

h=9.2-4+.3;

difference()
{
    cube([20,2h,2h]);   
    cylinder(d=15,h=h);

        translate([0,0,h])
        {
            cube([17,20,4]);
            cylinder(d=15,h=h);
        }
}
produces this after rendering:

but if you change  the value of h at the first line to

h=5.2+.3; 

(which is still the same number as above h=9.2-4+.3 and still equals to
5.5 )

restart openscad to reset cache, and rerender, you will get a different
picture:

anybody knows which version(revision) of openscad is last to be known to
not have this effect?

why do i get 2 volumes anyway?

Thanks for advice. Peter

Try this

h=9.2-4+.3;
h2=5.2+.3;
h3=5.2+.3+0.000005;
echo(h=h,h2=h2,h3=h3);
echo( (h==h2) ? "EQ" : "NEQ" );
echo( h-h2);

Floating point plays tricks, compounded, AGAIN, by echo rounding results.

Admin - PM me if you need anything, or if I've done something stupid...

Unless specifically shown otherwise above, my contribution is in the Public Domain; to the extent possible under law, I have waived all copyright and related or neighbouring rights to this work. Obviously inclusion of works of previous authors is not included in the above.

The TPP is no simple “trade agreement.”  Fight it! http://www.ourfairdeal.org/  time is running out!

Sent from: http://forum.openscad.org/