We always try to separate calculation routines from the user interface routines. This allows us to test parts of the program separately, but also to easily include proprietary calculations. Under MS-Windows for example the PVT, IPR, Multiphase flow correlations are in Dynamic Link Libraries (i.e. they are not within the main program). They are user-installable in the same way printer drivers are within MS-Windows. This can be very attractive to companies with a strong internal research program that wish to implement their calculations into our programs. In conclusion, we produce comprehensive engineer's tools, but also development platforms for researchers who can test, compare and implement their own calculations without having to worry about the user interface.