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Value Based on Generation Rarity or Ingredients: For items generated in the world, this is their rarity relative to the rarity of gold ore (so diamond ore is 2.4x as rare, etc.). For items which are crafted or smelted, this equal to the "Adjusted for Usefulness" value of their ingredients (the cost of smelting is not included) - literally counting these items as the sum of their parts. For mob drops, as I said, the rarity of mobs on generation is kinda meaningless, but the values for the items are based on how much of the item is dropped and how many mobs drop the item (string also acknowledges Abandoned Mineshafts at this point). Finally, if the item can be earned from a chest (dungeons, mineshafts, and villages. Strongholds are ignored), this is also accounted for, but the result is usually negligible.

Adjusted for Ease of Finding: This acknowledges ore buried deep in the earth is much harder to find than stuff growing on the surface. It also ups the value of biome-specific resources, and compensates for the inaccuracy of mob "rarity" per chunk. Once again, if an item can be found in a dungeon, mineshaft, or village chest, it gets a (negligible) reduction in value.

Adjusted for Capability to be Farmed: Probably the biggest problem in the current implementation of trading is its potential for exploitation - suddenly a sugarcane farm is a diamond pickaxe farm. Items are drastically reduced in value if they can be farmed (this includes hostile and passive mobs). The reduction in value is a factor (whereas most adjustments are just added or subtracted from the item's value). This factor considers how long it takes for a single unit (e.g. tree, 3-tall sugarcane, etc.) to grow, whether bonemeal can be used to hasten the process, and how much a single unit of the farm yields - all on top of an inherent 0.4x multiplier just for the fact that the item can be farmed. The process for mob farms is slightly different, acknowledging that animal farms need wheat, and that hostile mob spawners are ridiculously fast. If an item is farmable due to being a rare drop, this will also slightly factor in - however, auto-cooking farms are considered too negligible and thus do not further depreciate cooked items (its price is already devalued because the raw form is farmable). I have considered gold nugget (pigmen) farms negligible for the purposes of this chart.

Adjusted for Ease of Harvesting: This one counts mining, mob killing, and actual crop harvesting. For farms, replanting is considered here, but usually harvesting is easily automatable or otherwise instantaneous, and thus further depreciates the resource's value. For mining, pickaxe requirements are considered, and for mob killing, the mob's health and attack strength (in Normal mode) are considered.

Adjusted for Crafting/ Smelting: What it says on the tin. If an item is annoying to craft, it will be annoying to craft en masse; this very slightly increases its value. Smelting is more significant, accounting for the cost of 1/8 a lump of coal/charcoal, and the time required for smelting. The time it takes to sign a book-and-quill is also acknowledged here.

Adjusted for Usefulness: This is, in fact, the final modifier worth looking at if you wanted fair trades. Raw materials with many purposes get a large boost from this; their crafted results are thereafter reduced in value. Since an ore is worth the resource it drops, its usefulness is factored in there. Many things modify the usefulness of an item: for example, I considered a lump of coal and a block of glowstone as equally useful; this part is thus rather tricky and open to opinion. The usefulness of tools is based not only on their literal functions, but on their durability - armor also acknowledges its worth in terms of armor points. Food considers the hunger restored, and, to a lesser extent, saturation of the item (these values are applied to the raw form, because it is a precursor to the cooked form). If an item is farmable, even its usefulness modifier is scaled by the farming factor. Bottles o' Enchanting are interpreted as worth their average xp, which is itself considered from a number of factors which I used to determine the worth of an enchantment. Chainmail armor is considered equal in value to iron armor (before its usefulness adjustment is applied), with chainmail's durability and armor values.

Adjusted for Retail: Villagers can be stingy sometimes. Items sold to them are sold for less than their worth, and items bought from them are sometimes bought for more than their worth. This applies especially to the rich priests, but is also applied to diamond items to prevent trading from becoming overpowered. In the case of chainmail, its value is increased because the blacksmith is the only one who knows how to make it. In the case of saddles, however, the value is actually reduced because I presume Jeb intended for trading to be a more reasonable way to obtain the item (also, realistically, making hundreds of tiny chain-links is far more difficult than crafting a saddle . See? the butcher is still being stingier than the blacksmith!).

NPC Trader's Price: The value to look at for what all this would actually change. Villagers would have these prices rather than their current ones. If something costs more than 64 emeralds, the second offer slot may be used. If something costs more than 128 emeralds, emerald blocks will be used in one offer slot. Ideally, villagers would be able to calculate that an emerald block is worth 9 emeralds, and thus accept the two items interchangeably, but this is not necessary to fix trading. Note that the random ranges used here are based on the quantities involved, and capped at 5 in each direction, to not have excessive randomness in offers.

Fair Trade: Iron Ingots Per Stack: Let's say you're a human, not a squidificate. This is the value of a stack of an item, in iron ingots, based on the value in the "Adjusted for Usefulness" column - the retail adjustment is not counted here. If two players wanted to make a trade between a stack of the item and iron ingots, and wanted the trade to be fair (and ingore whatever items each player actually owns), then they might consider the number here to be a reasonable amount of iron. Bear in mind that I said "stack", not 64: ender pearls stack to 16, and many items do not stack (and thus, the price in iron is for one of that item).

Fair Trade: Iron Ingots Per Stack (Rounded): This one is just for convenience; iron is rounded to the closest value and stacked (each stack of iron is 64).