Ages of Technology (p. 6) offers a rough “average” of progress through history and prehistory, based on the ancient Near East, Greece, Rome, and Europe. Elsewhere in the world, technology evolved differently. Often it was slower; Paleolithic societies existed at the start of the 20th century! Occasionally it was faster. Define a society’s TL by the tools and techniques in common use there – not by the calendar date.

Different technologies don’t always advance in step. Some societies achieve a TL’s overall capabilities without all of its characteristic technologies – and sometimes without its signature technology! Variant societies can be described as “retarded in a science.” A society can also be “advanced in a science,” having one set of techniques usually found only at a higher TL; it might even jump from an early technology to a far more advanced one, skipping everything in between. And it’s quite possible for a society to be advanced in certain technologies but retarded in others. In extreme cases, a society’s TL may be a rough average of capabilities representative of three or four TLs. Judge a society’s TL by its overall function, never on the strength of a single technology.

Some examples:

Polynesian Navigators: The Polynesians had Stone Age technology overall, with pre-state social organization and without literacy. But they built boats with sails that could cross the Pacific, and developed navigational methods to guide their voyages. Treat them as TL0 with TL2 seafaring.

The Walls of Jericho: Archaeologists working at the site of Jericho discovered that its oldest relics date to 7000 B.C., in the late Neolithic. The original city covered 10 acres and had massive walls surrounded by a ditch. Its 2,400 inhabitants supported themselves by Neolithic farming and gazelle hunting. Jericho is TL0 with TL1 construction and fortification.

Mayan Astronomers: The Maya were the New World’s first civilization, building stone cities and keeping written records. But they didn’t have bronze, used few metal tools, and had no draft animals. On the other hand, their mathematics was sophisticated, with a symbol for zero; so was their astronomy. Treat them as TL1 with TL0 materials and TL3 mathematics.

African Metallurgy: The kingdoms of Sub-Saharan Africa didn’t pass through a distinct Bronze Age; their metallurgy went straight to iron. But they were otherwise organized like Bronze Age civilizations. Treat them as TL1 with TL2 metallurgy.

Medieval Medicine: In many branches of technology, medieval Europe was more advanced than the Roman Empire, from three-course crop rotation to weapons and armor. But for most of the Middle Ages, it didn’t support professional doctors, and it failed to advance beyond the Roman Empire in medicine – and in some ways fell behind it. Treat medieval Europe as TL3 with TL1-2 medicine.

Chinese Advances: Europe entered TL4 around 1450. But in the Middle Ages, Europe wasn’t the most technologically advanced society on Earth. Between 1000 and 1450, China developed cast iron; the magnetic compass; mechanical clocks; large seagoing junks that traveled as far as southern Africa; the printing press; paper money; and black powder. It’s plausible to put the start of TL4 earlier in China – perhaps in 1250, during the Mongol invasions.