Notes:
The analysis of the 'Top Ten' showing the percentage of calls and their coverage against the Single UNIX Specification.The top ten was derived from the top two in each sector (database, wordprocessor, cad/cam etc, networking app) else these would all have been database apps.
Even the worst of the ten has 96% of its APIs defined in the X/Open UNIX specification: only the remaining 4 percent will need to be examined for their portability.
(These calls are undocumented or 'proprietary' calls.)