A definitive list of what techs affect trade bonuses please

[Elephant]

No, I think it goes:
- Bonus doubled (before Nav or Inv)
- Bonus "normal" (until RR)
- Bonus drops 1/3 = 2/3 of "normal" (from RR to Flight)
- Bonus drops 2/3 = 1/3 of "normal" (after Flight)
What may have confused things was my saying "original", but the "original" is usually doubled before Nav or Inv.

[SlowThinker]

IMO the effect of techs must be independent (in scenarios you may have Flight before RR).
So Civ2 probably looks - do you have RR? Yes? Bang! The revenue is multiplied by 2/3, or 1/3 is substracted.
Do you have Flight? Yes? Another bang.

[Ell_man]

debeest said,

and one airport can increase the bonus "to 3/2," putting it back where it was before flight.

According to Solo's guide you need airports in both cities that are trading in order to get the 100% bonus(if on different continents) and the bonus is only 50% if the trading cities are on the same continent.

[Straybow]

The explanation of the effects were that bonus is calculated and truncated, then that bonus is divided by 3 and trancated to get RR/Fli penalty. If RR subtract penalty, if Fli subtract penalty.

Theoretically you (or more likely, an AI) could have Fli without RR in a regular game if you stole it from the other civ.

[debeest]

Right you are, Ell_Man. Airports in BOTH cities on the same continent will balance the flight penalty.