Thanks for replyes and advices, guys. I know that I can see mass on Launchpad and part counts in save/load screen. It's enough when you build your crafts with intuition only. But I'm trying to use some math and physics, I think it's more interesting than to do a couple of crash launchs to know would your rocket fly or not. And in this case I need to see dynamic Mass and Parts counts. We have a Center-of-Mass, Center-of-Thrust, Center-of-Lift already. Also we have a lot of engineering info for parts - and game use them in simulation! - so why wouldn't we have a little bit more info on our current projects? Game already use them, so all you need is to show them to a player. I think it's very easy to add, saying, a small button near Center-bla-bla buttons and a small window with info in right upper corner. Mods is good option when the game is not in beta status and is not update offen. And even then I don't like to use them just because I don't really know what they have changed in my game.