I have seven years of professional experience developing advanced Javascript solutions, as well as an MSC in Mechanical Engineering.
From your description, it sounds as if it can be done using Javascript only. I think the most important part of this project is to make sure that the results are 100% dependable and correct, since otherwise the consequences could be horrible. I believe the best way to achieve that is to make the application as simple as possible, not requiring any complicated communication etcetera. Since it sounds like no data ever needs to be saved, a pure Javascript application should satisfy that.
I could easily submit a lower quote if I did not care about testing, but in this case I expect 90% of the time to go into testing and verification, to make sure that absolutely every possibility is handled correctly. In addition, any unexpected situation must cause an error message rather than a result that could be wrong.
Let me know if you want to discuss more, I'd be very interested in seeing the data or formulas that should be used to generate the output.