Skill System & Product Upgrades

Besides levelling up the Factory and its Workstations, there are two main methods to permanently increase its productivity:
 * Research Skills: these are unlocked in the Skill Point Shop via Super Cash or District Cash and can be spent on a variety of passive abilities that boost various aspects of individual districts or all factories.
 * Product Upgrades: all the Products in any factory can be upgraded various times to increase their sales value, these upgrades remain in place after the factory was prestiged as well.