Typically, hardware cubes with marked centres use images or logos on the faces to designate what centre cubie(s) orientation is required for a solved cube. Application of such markings is generally restricted to just cubes of very small size.
The implementation and solving of cubes with marked centres in cubes of size 3 to a much higher size has been the focus of most of the Unravel program upgrades since 2012. Solving marked cubes of size greater than 3 is more complex than solving standard cubes of similar size.
When considering the application of marked centres to software cubes, a focus was placed on the following requirements:
There should be just one arrangement of individual cubies that constitutes a solved cube (compare with the unmarked case where centre cubies in each orbit on each face can occupy any one of four positions in the solved state).
Markings need to be as simple as possible and facilitate cube solving.
Cubie markings may impose a pixel penalty that limits the size of cube for which markings can be applied. Two forms of marking have been used for the Unravel program:
Numerical marking: Uses a black coloured number graphic in range 1 to 4 superimposed on the standard cubie colour in the background.
Corner marking: Uses a black coloured square a quarter the cubie size in area superimposed on the standard cubie colour in the background.
There is a direct correspondence between numerical and corner marking. A top left corner quadrant marking is equivalent a numerical marking 1, second quadrant to 2, third quadrant to 3, and fourth quadrant to 4. The following table illustrates these different forms of marking.
Marking | 0 deg | 90 deg | 180 deg | 270 deg |
Numeric | ![]() |
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Corner | ![]() |
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An upper cube size limit of about 32 applies for many monitors in common use when numerical marking is used. Corner marking (except for absolute centre cubies for cubes of odd size) is more difficult to use when unscrambling a cube than the numerical form but allows marking to be extended above the numerical marking limit.
Because transfer of cubies between orbits is impossible, the same 1-2-3-4 markings can be used for each orbit. With the exception of the absolute centre cubies for cubes of odd size, there are 24 centre cubies (4 per face) in each orbit. If n is cube size, there will be ((n - 2)2 - a)/4 orbits where a is zero if n is even or a is one if n is odd. Hence there are 9 orbits for a size 8 cube as shown below in images 1 and 2 for example.
For hardware cubes the cubie markings would change orientation as the face is rotated. However, with the exception of the absolute centre cubies for cubes of odd size orientation cannot be changed independently of position, so position defines orientation and vice versa. For software cubes (except for the absolute centre cubies for cubes of odd size) it is therefore necessary to change only position.
1 | ![]() |
Front face for a size 8 cube in the set state. |
2 | ![]() |
An example of a face for a size 8 cube after scrambling. |
3 | ![]() |
Front face for a size 9 cube in the set state when a numerical graphic is used to mark the rotation of the absolute centre cubie. |
4 | ![]() |
An example of a face for a size 9 cube in the scrambled state when a numerical graphic is used to mark the rotation of the absolute centre cubie. |
5 | ![]() |
Front face for a size 9 cube in the set state when a corner graphic is used to mark the rotation of the absolute centre cubie. |
6 | ![]() |
The identical example of a face for a size 9 cube in the scrambled state when a corner graphic is used to mark the rotation of the absolute centre cubie. |
7 | ![]() |
Front face for a size 8 cube in the set state when this size cube is used to simulate absolute centre cubie rotation for a size 7 cube. |
8 | ![]() |
An example of a face for a size 8 cube after scrambling when this size cube is used to simulate absolute centre cubie rotation for a size 7 cube. |
For cubes of odd size the absolute centre cubies are subject to restricted movement - they can only occupy 6 possible positions (one on each face) whereas other centre cubies can occupy 24 possible positions. To track their rotation, numerical marking as in images 3 and 4 or corner marking as in images 5 and 6 can be used. The default for marked cubes is to use corner marking for absolute centre cubies and numerical marking where possible for other centre cubies. When the system shown in images 3 to 6 is in use the absolute centre cubie images are subject to change or possible change for every quarter turn of the cube.
An earlier form of centre cubie marking that used a one size up cube to simulate absolute centre cubie marking is still available and is illustrated in images 7 and 8. With the one-up simulation the program does not permit any move that would allow relative movement between the two most central layers. In all other respects it behaves as a size 7 cube with central pairs of centre and edge cubies behaving as single cubies. For image 8 note that the 1-2-3-4 sequence is maintained but the central block has been rotated. For non-absolute-centre-cubies, numerical marking is omitted on the cubie on the clockwise side of the central pairs. Multiple images for the absolute centre cubies are not required for this option - the rotational status of the absolute centre cubie is defined by its cubie positions. The program does not allow the one-size-up marking option to be swapped with that used in images 3 to 6 for a partially unscrambled cube.
The selection of which of the marked absolute centre cubie rotation display options the user adopts is provided by the Unravel Options dialog and the cube size to which the corner cubie style can extend the marking option above the numerical marking limit can be changed via the Program Settings dialog.
The full block of centre cubies can be rotated relative to the surrounding corner and edge cubies. The orientation of the block of centre cubies is given by the single number "1" marker on the left upper corner on each face for the set cube. The nearest centre cubie to that marker must have a "1" indicator for correct final alignment. Macros are available to correct for any such misalignment. However, if the user sets the white face at the bottom and the red face on the front and follows the approach to solving provided herein, the user will never experience this form of misalignment. Hence, although the availability of the marker is useful, it is not essential. If there were no marker and the user adopted a different orientation of the whole cube there would be 2048 possible arrangements for the solved cube that would appear correct.