IGB uses a 0-based coordinate system, so each chromosome starts at position 0 and ends at -1 of the length of the chromosome.
For example, the human genome H_sapiens_Dec_2013 (hg38) first chromosome has a length of 248,956,422. In IGB the first base position is labelled as 0.
The last base position is labelled as 248,956,421.
While many file types use a 0-based coordinate system, some, such as Wiggle, use a 1-based coordinate system. The coordinate position listed in a Wiggle file is +1 when compared to the coordinate in IGB.