Finally something I can apply my expensive ChemE degree on :')
These diagrams were always the worst to use, far too busy and usually printed on cheap paper making it impossible to distinguish one line from the other.
Basically its a diagram is relating the energy required to change the state of something (usually water) and while in theory is amazing and clean in allowing you to determining enthalpy necessary for a state at a constant pressure.
In practice though can get really messy especially with more variables in play, as shown with the temperature decreasing as the balloon altitude increases.
From my very limited understanding that’s kinda what they tried with the BMD lineup. Problem is because they’re for airborne use they end up too light to protect anything, and loaded with ATGMs, a 100mm cannon, and a 30mm for squirting lighter targets. Basically on first hit it goes up like a Christmas tree lol