International
Tables for
Crystallography
Volume F
Crystallography of biological macromolecules
Edited by E. Arnold, D. M. Himmel and M. G. Rossmann

International Tables for Crystallography (2012). Vol. F, ch. 11.4, p. 290   | 1 | 2 |

Section 11.4.8.1. Global and local scaling

Z. Otwinowski,a* W. Minor,b D. Boreka and M. Cymborowskib

aUT Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390–9038, USA, and bDepartment of Molecular Physiology and Biological Physics, University of Virginia, 1300 Jefferson Park Avenue, Charlottesville, VA 22908, USA
Correspondence e-mail:  zbyszek@work.swmed.edu

11.4.8.1. Global and local scaling

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In principle, global scaling can be followed by local scaling (Matthews & Czerwinski, 1975[link]). Local scaling is mostly applied to calculate differences of phasing signal, where it is assumed that a group of measurements, e.g. those close together in reciprocal space or detector space, should be on a similar scale. A flexible parameterization by the exponential modelling allows for a good description of all kinds of smooth corrections. Local scaling is much more limited in terms of what type of smooth variation is being corrected for, so it is unlikely to provide additional benefit to the general scaling method described here. In practice, if there is an improvement from such procedures at the stage of heavy-atom search, it implies that the scaling parameters for global scaling were not properly chosen.

References

Matthews, B. W. & Czerwinski, E. W. (1975). Local scaling: a method to reduce systematic errors in isomorphous replacement and anomalous scattering measurements. Acta Cryst. A31, 480–487.








































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