This is part of a a collection of summaries on the fourteenth century.
The livre is the French word for pound, nominally of silver though by this time the currency had been greatly debased. (James Blish's Doctor Mirabilis mentions that a hundred years earlier English money was the only kind that hadn't been massively debased.) In fact there were several kinds of livre but the livre tournois was by far the most important, and I'll drop the qualifier from now. Equivalent words in other languages are pound (English), florin (Florence), ducat (Venice), franc (France?), écu (France?) and mark (Germany). It shouldn't be assumed these were all of equal value in the period in question, since they'd all been debased by different amounts. The "nearest things to a standard" were the Venetian ducat and the Florentine florin, each at 3.5 grams of gold (which would be worth thirty-something Australian dollars at time of writing, no reflection on purchasing power intended). The livre was made up of twenty sous. A sou (in English, shilling) is divided into twelve pennies.
Tuchman's advice is "simply to think of any given amount as so many pieces of money", which strikes me as negating all value in giving a price in the first place. She remarks of fourteenth century chroniclers that they "did not use numbers as data but as a device of literary art to amaze or appal the reader" and perhaps this is Tuchman's intent as well.
Carlson says that the silver penny was standard, and values everything else in terms of it. But that only makes sense if by a silver penny he means a silver penny that hasn't been debased, so we may be comparing apples and oranges here. That is, my use for the data may not be the same as Carlson's, and Carlson's data may not serve my purpose in this respect. Taking his figures at face value (no pun intended) the livre and the pound are equal in value, and the florin worth only 30% as much.
Dunnigan values everything in ducats, and gives the pound as 600, the florin as 300 and the livre tournois as 133, i.e. 4.5 livre to the pound. These clearly aren't the same ducats as Tuchman talks about, which seem to be worth quite a bit. Dunnigan estimates a ducat to be worth US$1 in the early 1990s. Of course, that's a highly dubious kind of comparison: a million ducats in 1340 would have bought a very large number of loaves of bread, but not a single course of penicillin. Dunnigan's valuation of the ducat makes Shylock's loan of a few thousand ducats seem like a petty cash transaction.
The figures generally apply to France or England in the 1340s, unless otherwise specified. After the black death salaries rise, there are cases where they double or treble. There were laws prohibiting rises, or limiting them to one-third above prior levels, but at least the first seems to have been unenforceable.
Other material can be found on my home page, including some on alternate history. I welcome feedback at David.Bofinger@dsto.defenceSpamProofing.gov.au (delete the spamproofing).