Yes, one every turn is definitely possible, with the SSC and some good trade routes.
One per turn should be demanded, at about RR or so, at deity... esp. on a large map. The SSC is nice, but also not necessary for one per turn, as long as you do have the good trade routes. Freight and caravans alone, if aggressively delivered (and defended) can carry one advance per turn. Ship delivery to foriegn empires is most rewarding. Ship chaining can allow use of the JIT (Just In Time) management theory, btw.
What is the shortest time you've manged between discoveries? I got up to one every two turns - is one EVERY turn possible?
As a minimum, I expect one turn per advance in every "regular" game. I've been able to sustain up to 6 (or maybe 7) advances per turn in a GOTM last year, durint the late tech tree/early FT range. One advance due to Freight, and the rest due to research.... but you need to play a non-purple civ, keep the puple civ alive, be supreme, and gift the purple civ to max your research rate.
In GOTM 18, I'm just past AD 1000, and have been sustaining one advance per turn, each turn, and every single turn, for over 300 years. This is in a Fundy goct, with just a single Scientist (2 beakers, in Fundy). The 1800 beakers for an advance come from freight. The scientists puts it over the top.
Dat dey dooo! With 30+ Triremes (or caravels).
For big bonuses, remeber to additional things to Duke's post....
1. Get the max distance (diagonals are 1.5) between source and destination cities.
2. Get the max
base arrows in the city(s). If your Colossus city is doing it's job, this base should be 70+ (subtract the 3 route values to get base, or count the individual arrows). Since no other pre-flight city is near this amount, the dominant factor is the Colossus city trade arrows. It does not make much difference whether your destination city has 2 arrows or 10 arrows.... so go for a foriegn target to avoid getting your valuse cut by 50% for trading with yourself.
You can follow links from my sig block (go to PD) for lots more trade discussion

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