I'm running a test game. I toggled AI and set timeout so that the game runs for a while, then re-toggled myself back in. Now I'm running Despotism with 0% Science and for a few turns I've been losing tech due to unmet upkeep. And the numbers are very wierd.
For starters, divider is 1000 and tech_upkeep_free=3.
Looking at a techtree with only 4 tech discovered:
Pottery
Iron Working
Writing
Monarchy
Bulbs needed for upkeep: 36
After pressing Turn Done:
lost Iron Working
Bulbs needed for upkeep: 35
After pressing Turn Done:
lost Iron Working
Bulbs needed for upkeep: 26
After that, any other turn, "current bulbs" started going further and further into the negatove and no techs were lost anymore.
Also, what happened to tech_upkeep_free? With these numbers, I was supposed to avoid paying tech upkeep until I have researched 3000 worth of bulbs and that actually does happen when you're researching, that is, accumulating bulbs.