Your primary currency for hiring advisors, changing laws, and justifying war goals. It typically accumulates at 1–2 points per day.
Factories gain efficiency the longer they produce the same equipment. Retooling to a new tank model causes a temporary "efficiency cap" drop. heats of iron 4
Always keep your Industrial and Electronic Engineering techs up to date, as they provide multiplicative bonuses to everything else. Your primary currency for hiring advisors, changing laws,