WTRTI (War Thunder Real Time Information) is a helper program created by GitHub User MeSoftHorny, available on the project's GitHub page here. With it, you can add custom indicators in addition to the built in ones, either by adding existing but not implemented State variables, or by using a LUA script to do math on any number of State indicators to return a customized indicator.
For example, I regularly use SEP (Specific Excess Power, essentially how many m/s of power the engine is producing that can be used to either increase the speed of the plane or climb with.) and the Climb rate (labeled as the State Vy), to help determine an optimal climb rate, so that I can get to speed then climb at the max speed possible without losing speed by keeping Vy below SEP. To assist me in this, I created a custom indicator I called Excess Power, shortened to XSPWR using a lua script included in this.