I don't think I could call this theory but it is useful.
If someone showed you a slide rule and said it was for ‘engineering’ would you say ‘well it doesn’t really do engineering’?
A slide rule would be more analogous to a musical instrument. If you want an analogy between this app and engineering in the slide rule days, it would be closer to a pocket sized reference book of log tables and formulas.
Perhaps this is being pedantic but these sorts of distinctions are fairly important, understanding what you do and do not know will make you more effective at learning and help you identify what is of use for you to learn. As someone who taught this stuff you should know that the ones who are most difficult to teach are the ones who think they already know.