The Sample Type flyout lets you choose which geometry to display in the active sample slot.

This flyout has three or four buttons:
-
Sphere (the default) Displays the material on a sphere.
-
Cylinder Displays the material on a cylinder.
-
Cube Displays the material on a cube.
-
Custom Displays the material on a custom object.
This button appears only if you have used the Material Editor Options dialog to specify a custom object for sample slots.