At present, several are in their final testing stages, being cross-checked for mathematical inconsistencies, bugs, etc. More effort is spent on later quality-control than on producing the first useable version of a program. It's good practice to put a supposedly finished program on the shelf for a month or so, allow one's mind to forget it, concentrate on something else such as producing this web site, even spending some time on the 'air'. It is surprising how previously unnoticed defects then become obvious. Until recently I have never actually finished a computer program.
All programs ask for a set of numerical values which describe or define the matter in hand.
Often the data are physical dimensions plus a choice of operating conditions. This initial array of data is always on view at the top of the screen. When a set of results has been computed it is displayed in the lower part of the screen. Immediately the question is answered. A similar question can then be asked about any other parameter.