Click on any "General Position Symbol" (one of the circles). The coordinates of that position will appear . Addition to or subtraction from any coordinate (x, y, z) is allowed by translation. (examples: x = x + 1, y = y - 1)

                 Fractional Crystal Coordinates                      General Position Diagram                               orientation of cell



The 0, 0, 0 and 1/2 , 1/2 , 0 above the coordinates for the general positions indicate the centering operation. This is a C centered cell. The C face is the ab face, in the plane of the screen in this case.. The centering operation takes an object at x, y, x and moves it to 1/2 + x, 1/2 + y, z. Notice that the four symbols at the four corners are identical by translation, and that the four symbols in the center are identical to those at the corners by the centering operation.

The object at position 1 is moved to position 2 by a 2-fold screw parallel to c. It is moved to position 3 by a 2-fold rotation at z = 1/4: consider that an object at z = 0 would be rotated to z = 1/2, and thus an object at +z would be rotated to 1/2 - z. Finally, the object at position 1 is moved to position 4 by a 2-fold rotation parallel to a at y = 0.

Not that all symmetry elements here are rotations, so there are no circles with commas.