this game is not logical, the more you advance, the more an upgrade is expensive. So, it means you will have a betteer productivity with 2 small units than with one 2 time bigger. In an economic way it is totally unbelieveble. Normally the biggerf is your production unit, the cheaper is the price to produce the same quantity. Here it is the opposite. An economic game without economy of scale, totally irrational.
 "Night Vision"){kind=icon}
 "Gold Rush"){kind=icon}