- Number of parts (
**1**,**2**,**3**or**4**) - Palindromic symmetry (
**P**) (reflection about a horizontal axis) - Double symmetry (
**D**) (rotation through 180 degrees) - Left-right glide reflection symmetry (
**R**)

The numbers of extents by symmetry group are:

1 | 2 | 3 | 4 | Total | |||

none | 75 | 2 | 0 | 0 | 77 | ||

P | 53 | 3 | 4 | 2 | 62 | ||

D | 10 | 1 | 0 | 0 | 11 | ||

R | 2 | 0 | 0 | 0 | 2 | ||

PDR | 7 | 0 | 3 | 0 | 10 | ||

Total | 147 | 6 | 7 | 2 | 162 |

The number of extents is reduced even further if one ignores "trivial variations" involving Kent or Oxford places. Thus, the place notation fragments x12x and 34.12.34 may always be used interchangeably, and similarly for the pairs x34x, 12.34.12 and 34.12.34, 12.34.12. Taking this into account, there are only 29 essentially different extents, given here in a format emphasising the symmetries.