Can't make any sense of upgrade costs

[CivilizationAce]

Anyone got a clue?

I'd like to be able to manipulate them so upgrades for my new units cost at least approximately what I have in midn, but there seems to be no logic to them. I can't take the construction costs and apply any formula that will work on all the units.

 

[Aldollin]

i am pretty sure its not based on construction cost difference but on combat strength (at least thats what i have heard)
and it would explain something like the upgrade cost from eagle warrior to swardsman beeing lower than from a regular warrior
again, havent tested it, but it is something ive heard multiple times

 

[CivilizationAce]

Slinger (ranged str, RS, 15) to Archer (RS25) costs 30
Eagle Warrior (Str28) to Swordsman (Str36) costs 45
Warrior (Str20) to Swordsman (Str36) costs 80

That suggests that if the cost is a*target str-b*source str+c or aT-bS+c then solving for a, b and c we get
575/88T-35/8S-745/11

However, I doubt they'd use such esoteric numbers. I suspect that it's a simpler calculation rounded to the nearest 5. A problem is the 35/8. That equates to 4.375, which isn't close enough to 4 that if I change it to that I'd get the same result. Worse the -68 or so would surely make no sense – I was expecting c to be an overhead cost not discount. In short I think further speculation along these lines would require more information.

Do you remember where you heard it?

 

[Aldollin]

No, dont know where i heard that, might be completly wrong

http://civilization.wikia.com/wiki/Upgrade
This website claims the upgrade cost is
20+3*(differenze in produktion cost)

 

[NameArleadyUsed]

max { | PROD_1 - PROD_2 | * GlobalParameters.UPGRADE_NET_PRODUCTION_PERCENT_COST , 30 }

 

[NameArleadyUsed]

20+3*(differenze in produktion cost)

How would it, by the way, allow for having 30 upgrade cost for example?