You get a 20% bonus for having the "must-have" techs...
I.e.
Mining you must research 100% of the beakers shown in the Techtree, it has no prerequisites
Bronzeworking has ONLY 1 must-have tech, mining. But you do get +20% for it.
Which means that say Mining is 100 beakers and BW 240, while you are generating 10 beakers/turn (including the 1 free beaker!)
Mining is 10 turns, while BW is not 24 turns but 20 turns.
Now you get an additional 20% per "optional" tech.
I.e.
Writing can be researched with only Pottery (20% bonus tho)
So at 10 beakers/turn and writing at 240 beakers would make it 20 turns (20*10 = 200 raw beaker cost)
Now research AH for an additional 20% bonus for 17 turns (171 raw beakers)
Now research Priesthood for another addition of 20% bonus for only 15 turns (150 raw beakers).
Effective discount on Writing after Potter+Priesthood+AH vs Pottery only = 50 raw beakers.
In short you can say that each white line you research prior to that tech will give you a "bonus" (not a direct discount) of 20%.
Note that some techs (Devine right and Astonomy) beeing two of them dont have any white lines. These NEVER get the 20% discount...
Read the
full article by Requies in the
War Academy, lots of usefull stuff there.
Something you might not know either... You also get a simular bonus for researching a tech that is known by a civ you know. This bonus seems to be roughly 3% per civ you know that knows the tech.
Again this bonus is calculated over the # of beakers you produce, not deducted from the beaker cost of the tech. And before applying to the tech it is actually rounded down.
So 10 beakers/turn + 3% * 3 civs knowing = 10.9 = 10 beakers/turn.
So it never realy adds up early on... but 100 beakers/turn * 3% * 3 civs = 109 beakers. So there, a little later on in the game it is helping ... even if a little.
This mechanic explains tho why:
- it can be easier to catch up to stay ahead (you get bonusses)
- techs devaluate in trade once 2 or 3 civs know it (it gets cheaper to research it yourself)
- Beelining can be expensive.
Bad "beelining" example, where you research pre-req techs just after the "beelined" tech (Please forgive me for skipping a tech or 2 but you get my drift I think) :
wheel > Agriculture > Pottery > Fishing > Writing > Priesthood > AH > Hunting > COL > Currency
Offcourse beelining can bring its own rewards, but can also be costly if you dont take advantage of it. Like in above example only starting to build a Library after researching Hunting.
The "cheapest" way of researching the techs would be:
Wheel > fishing > Agriculture > Hunting > Pottery > AH > Priesthood > Writing > Currency > CoL
1) research the 100% cost techs first (getting the 20% or more bonus on the most beakers)
2) Research the techs in the "proper" order