The chemical shift index or CSI is a widely employed technique in protein nuclear magnetic resonance spectroscopy that can be used to display and identify the location (i.e. start and end) as well as the type of protein secondary structure (beta strands, helices and random coil regions) found in proteins using only backbone chemical shift data  The technique was invented by David S. Wishart in 1992 for analyzing Hα chemical shifts and then later extended by him in 1994 to incorporate C backbone shifts. The original CSI method makes use of the fact that Hα chemical shifts of amino acid residues in helices tends to be shifted upfield (i.e. towards the right side of an NMR spectrum) relative to their random coil values and downfield (i.e. towards the left side of an NMR spectrum) in beta strands.  Similar kinds of upfield and downfield trends are also detectable in backbone C chemical shifts.