Table 1. Internal phase residuals of all rectangular plane groups for an image of an aquaporin-0 (AQP0) crystal in a pure cholesterol membrane.

Space group	Phase residual (degrees)*	Number of comparisons	Target residual (degrees)†
p1	12.5 ‡	240
p2	33.8	120	17.8
p12b	14.5 §	108	12.9
p12a	31.7	109	12.9
p121b	83.7	108	12.9
p121a	80.0	109	12.9
c12b	14.5 §	108	12.9
c12a	31.7	109	12.9
p222	27.0	337	14.4
p2221b	60.0	337	14.4
p2221a	68.2	337	14.4
p22121	69.7	337	14.4
c222	27.0	337	14.4
p4	26.3	352	14.3
p422 ¶	24.5	791	13.3
p4212	62.6	791	13.3

Internal residuals were determined using the ALLSPACE program (Valpuesta et al., 1994) using spots from IQ1 to IQ5 to a resolution of 6 Å.

^*Phase residual versus other spots (90° random).

^†Target residual based on the statistics taking Friedel weight into account.

^‡Note that no phase comparison is possible in space group p1, so that the listed numbers are theoretical phase residuals based on the signal-to-noise ratio of the observed diffraction spots in the Fourier transform.

^§Within 5° of target residual.

^¶The symmetry indicated in bold was used to calculate the final 2D projection map.