Comparison of 16 Å resolution envelopes for Na+-NQR obtained with different protocols after 15 cycles of phasing. (a) Overlay of envelopes calculated from a single data set with missing reflections in the low-resolution sphere (magenta) or from the same data after the addition of 13 reflections estimated from a different crystal (yellow). The observed differences illustrate the importance of the completeness of low-resolution reflections. (b) Overlay of envelopes obtained applying slightly different phasing parameters. Both envelopes are essentially the same, underlining the robustness of the method.