Congratulations on finishing your app. It's targeting a very very very specific user base, but it's neat all the same. I'm not sure you'll get much love on HN...

Maybe you could add some bulk with more mechanical equations for real world usage, then flesh it out into a mathematics-for-engineers application of some sort. I'm sure no one remembers all their Mechanical formulae off the top of their head!

One thing I would say is have a look at Holo UI. The cupcake/donut styles are looking a bit worse for wear nowadays.

Code on!

Thanks for the tip on holo! And yeah, my end game is to kind of get together a bunch of apps that are useful for racecar builders. All of them together, well tested and well explained, might be worth someone paying for.

Congratulations on finishing. I'd agree with jonsherrard, try to upgrade to Holo UI when you get a chance. Your app will instantly look better. Also if you learn something about android graphics maybe you could provide a dynamic image of the spring that changes as you enter values so people know if they're making a mistake (sounds hard, but possible).