Research is super fun, but can seriously unbalance the game if a player gets lucky with their first couple rolls. Therefore, we play that the player chooses which tech to research, however better techs have a lower chance of being successfully researched.
The mechanism of researching is the same, you buy research tokens (dice rolls), roll for success, if none hit the tokens are banked for next turn and can roll again at no cost, if successful the tech is gained and the tokens are removed and must be rebought to do more research . The cost of each token (die roll) is increased to 8 IPC (normally is 5). But, tier 1 techs will be successfully researched with a roll of 3 or lower, tier 2 with roll of 2 or lower, and tier 3 with roll of 1:
(3/6 chance) 1. adv artillery, inc factory prod . || mech infantry, war bonds
(2/6 chance) 2. long-range aircraft, radar . . . . || paratroopers, rockets
(1/6 chance) 3. heavy bombers, super subs . . || jet fighters, improved shipyards
To balance out how multiple techs are gained, we separated complimentary tech into opposing groups to prevent them from easily being researched too quickly back-back and becoming OP. To research a tier 2 or 3 tech at least one tech from the tier below must be already obtained from WITHIN the branch. Note, the techs are separated into left and right branches.
So to get heavy bombers (left, tier 3), you could research adv artillery or factory prod (left, tier 1) then radar or long-range air (left, tier 2). Then, to get jet fighters (right, tier 3), you’d have to also research 2 corresponding lower tier techs in the right branch, because adv artillery/radar/etc. don’t count towards the necessary lower tier techs for the right branch.