Quote -  Nothing in nature has a perfectly circular specular highlight like you'd find on a Phong shader, so Anisotropic is probably the most underrated specular type of all.

Traditionally it is used to create brushed metal, stainless steel but can also be used for (procedural) hair or any other object that has "irregular" specular highlights.

Normally xDir, yDir and zDir (don't know the exact names in PoserSpeak) distort the direction of your highlight while highlight size will affect intensity or width. Really the best way to understand this is to load a sphere, apply an Anisotropic and tweak the settings.

you think i didnt do tests? :)
thats why i opened this thread. there are no changes. is my poser software broken or wht?there is no change in the redner when i change xDir, yDir and zDir