Tech Levels are a way to distinguish different items by the way they are manufactured. In the post-apocalyptic wastelands of the Mutant Future, the enviroment is littered with high-tech wonders of the past, and current manufacturing techniques has been reduced to a primitive state to one degree or another. Even with artifacts form the past and conventional items, there are different levels to be found with both.
As the Mutant Future rulebook lists no hard, definitive level grades, it is up to Mutant Lords to establish their own system, if at all (it is not a requirement for play). The rulebook assumes that the default level of technology is around Europe's Early Middle Ages — a pre-gunpowder era, with wide use of metal weapons, along with bows and crossbows — but Mutant Lords can freely change this. The rulebook outright states that the technology form before the apocalypse was an advanced civilization akin to The Jetsons, although it also list modern items in the artifact lists.
Here is a good breakdown of Tech Levels (with alternative names):
TL0 — Primitive (Crude) Technology: This level is mostly seen with nomadic hunter-gatherer societies, with no permanent sites of industry, so items have to be crafted on-the-spot with anything at-hand. Typical items include Stone Age equivalent weapons and tools (made of cut stone or jagged scrap metal), any crude item improvised from more advanced technology (e.g. A sheet of duralloy crafted by high-tech manufacturing can be made into a sturdy shield with some vines or leather for a grip), or any byproducts of nature (mutant barriers used for healing, explosive nuts, paralyzing venom for blowgun quills, etc.).
This is found with any tribal village, or tool-using mutants of low intelligence. Mutant Lords can rule that players characters start at this level to make the game more interesting, or to highlight a character's Barbarian archetype.
TL1 — Basic (Standard) Technology: This level requires permanent workshops with skilled craftsmen. They include blacksmiths, leather workers, woodworkers, and so on. Such industry would also require supplemental services that would make their work possible: scrap collectors, animal skinners, lumberjacks, carpenter, farmers, and so on.
This is the default for players characters, and can be found in most towns and all cities. Although they could improvise simple items from advanced technology like primitive folks. The items they create would be better in quality and manufacture. For example, making a firearm with basic technology is possible, they would take the form of primitive hand-cannons or muskets with unique specifications (e.g. no ball-size or barrel-width standards). Unlike primitive people, settled folks are not as dependent on nature to make full use of natural byproducts.
TL2 — Modern (Industrial) Technology: This is a level of manufacturing that requires modern industry, with factories, power-plants, machine shops, laboratories, and motorized transportation. This is not to be limited to just modern 20th century devices, but also early industrial and even Steampunk-styled inventions.
By Mutant Future's artifact standards, this is antique technology, and should be treated as museum pieces, unless the Mutant Lord rules that they where still widely used before the apocalypse. A community achieving this level of technology on their own would be a major feat, and it would, form a technological standpoint, become a powerful force within it's region. This type of community should be extremely rare, and the items produced by them should not be available to outsiders, do to the risk of outsiders turning their own weapons on them to take their industrial secrets for themselves. Widely available modern technology would also change the balance of power in a setting. An understanding of modern technology could be used to build crude, bulky versions of advanced technology. For example, a modern-styled Laser Rifle would be large enough to be treated like portable artillery with a crew of two or three men, with the same damage output as a standard Laser Rifle, but with more energy usage.
TL3 — Advanced (Futuristic) Technology: This is the type of technology Mutant Lords have to dream up, or read/watch science fiction for inspiration. It is almost like magic, but with some (pseudo)scientific explanation for how it works. Robots, flying-cars, rayguns, spaceships, cybernetic implants, mechanically-enhanced power armor, and so on.
A community achieving this level of technology on their own would be an outstanding feat of technological innovation and understanding! The only community that would likely have any Advanced Technology manufacturing would likely be a completely isolated and unknown city that has been using (and relying on) the sophisticated machinery that makes their lives possible (life-supports systems, hydroponics bays, fabricators, databanks, etc.) well before the apocalypse. In a semi-barbaric world like Mutant Future, possession and mastery of advanced devices could turn even a weak, helpless person into someone who is as feared and respected as a powerful Wizard!
TL4 (TLX) — Alien (Xeno-) Technology: This is a level of technology that would be foreign even by the standards of the pre-apocalyptic era. Such devices would be strange in use and appearance, and would likely defy any understanding for reverse-engineering. This level would likely be included in settings that was subjected to an alien invasion. This can range form the organic, but somewhat recognizable devices used by the Spacy Jockeys form the Alien movies, to the weird-looking artifacts used by ancient races in the Lovecraftian Mythos (Primordial Ones, Elder Things, etc.).
If used, Mutant Lords are encourage to add, remove and alter from this list as they see fit, so suit their own setting.