Redbad
should have shaved
The worth of a certain tech for a certain AI is related to the amount of beakers that that AI has to put into science to research it. So a tech which requires more beakers to research is worth more. But the amount of beakers is not a fixed amount.al_thor said:370 AD - America has Chivalry. He will trade Chiv for Invention, but I'm not selling.
490 AD - 7GPT, 6G from China for Mono.
500 AD - 27GPT, 114G from Zulu for Invention (America will no longer give Chiv for it). Hittites already know Invention.
510 AD - Now, THIS I found to be weird. 122G, Chivalry from America for Invention, whne he wouldn't even trade me even up for it just last turn!![]()
Firstly a civ can be researching that tech himself, which will cause the tech to become less valuable to him over time.
Secondly the knowledge of a tech can be spread over more civs. The more civs know a tech the less beakers it requires to research.
The second happened in your situation.
In 370 you knew invention and America knew chivalry. A deal could be made.
In 500 invention was also known by Zulu and Hittites. This will decrease the number of beakers to research it for America substantially. And maybe America even is researching it himself. So now a deal can't be made.
In 510 I suspect one or more AIs got knowledge of chivalry, thus decreasing it's value. And a deal can be made again.
BTW. the above is not always as apparent: sometimes the price you get for a tech is not the value it has for an AI, but simply the most that AI can offer you. In the latter situation selling a tech to another AI will have seemingly no effect on the price.