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A limited-range, step-scan method for rapid diffractometer data collection is described. The data are reduced in a two-pass procedure. First, the step data from the more intense peaks are fitted by a Gaussian function yi = C1 exp [-(
- xi)2/C22], where C1 is the peak maximum, C2 is proportional to the peak width and C1C2 is proportional to the integrated intensity. Because the peak widths may vary appreciably over the range of data observed and cannot be determined very precisely for weak reflections, an empirical function is determined from the more intense reflections in the first pass and the calculated peak widths are used for all reflections in the second pass. Comparison of data obtained by this method and the usual full-scan technique shows that comparable precision can be obtained even when the limited scan range data are collected at twice the rate of the full-scan technique. The method has been used to collect data for five proteins and typical results are cited.
- xi)2/C22], where C1 is the peak maximum, C2 is proportional to the peak width and C1C2 is proportional to the integrated intensity. Because the peak widths may vary appreciably over the range of data observed and cannot be determined very precisely for weak reflections, an empirical function is determined from the more intense reflections in the first pass and the calculated peak widths are used for all reflections in the second pass. Comparison of data obtained by this method and the usual full-scan technique shows that comparable precision can be obtained even when the limited scan range data are collected at twice the rate of the full-scan technique. The method has been used to collect data for five proteins and typical results are cited. 
