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IUPAC-IUB codes
The IUPAC-IUB codes are used to define multiple nucleotide possibilities in one position. The table below indicates the definitions. When editting basecalls during anlysis you can also enter the single nucleotides (GATC) and SBTengine will automatically change it into the correct IUPAC-IUB code (see Editing topic). Alternatively you may use the diagram shown below. You can access this diagram from the Sequence Overview tab be pressing the F2 key and exit it again be pressing the Escape (Esc) key.

How to interpret the IUPAC-IUB codes diagram?
The four single nucleotides (GATC) are color coded and located in the middle of the diagram with the IUPAC-IUB codes around them. Just look in the diagram which IUPAC-IUB code grasps which nucleotides. For example, the AT are grasped by the W, whereas the TG are grasped by the K. On the other hand, the TC are lined up by the Y, whereas the AG are lined up by the R.
The H grasps ATC and the D grasps ATG.  You could also say that the outher H arrow points left so it encodes every single nucleotides except the one on the right side (G). Another trick is the rule that the H is preceeded in the alphabet by the G. So the H encodes every single nucleotides except the one that preceeds it in the alpahbet (G). Both rules also apply for the IUPAC-IUB codes D, V (the U preceeding the V encodes for the RNA Uracil so the next in line in the alphabet is the T) and B.

Nomenclature Committee of the International Union of Biochemistry (IUPAC-IUB) 
Nomenclature for Incompletely Specified Bases in Nucleic Acid Sequences
Recommendations 1984 
World Wide Web version Prepared by 
G. P. Moss
Department of Chemistry, 
Queen Mary University of London, 
Mile End Road, London, E1 4NS, UK
g.p.moss@qmul.ac.uk


These Rules are as close as possible to the published version [see Biochem. J., 1985, 229, 281-286; Eur. J. Biochem., 1985, 150, 1-5; J. Biol. Chem., 1986, 261, 13-17; Mol. Biol. Evol., 1986, 3, 99-108; Nucl. Acids Res., 1985, 13, 3021-3030; Proc. Nat. Acad. Sci. (U. S.), 1986, 83, 4-8; and in Biochemical Nomenclature and Related Documents 2nd edition, Portland Press, 1992, pp 122-126. Copyright IUBMB; reproduced with the permission of IUBMB]. If you need to cite these rules please quote these references as their source.

For more information please look at the full text at the web site of IUPAC-IUB