Explanation of the apparatus:

[To return to the demonstration page in its careted overlay version: FW: 48.
To jump to the basics of the notation system or its details: authorized changes between levels; changes within levels; TDs and IMs: transmissional departures and instructions missing; further symbols.]

    The representation of the revision history of Finnegans Wake shows additions, deletions and changes from first draft (level 0) through to the final corrections Joyce made in 1940 on unbound pages of the published book (level 13). 1  The list of levels may be seen here,  and also in the dialogue box appearing when one runs the "reduction program", fw.exe, in the electronic version. This program allows the user to display , for any Wake page in chapters 2-4 (FW: 30-103):     The representation is not a diplomatic transcription of the documents but a telling of the genetic story. Therefore:
    Changes which appear in transcriptions made by typists and typesetters and which are not authorized by Joyce's holograph or other surviving instruction are marked using two systems between which the user of the electronic version may choose. (It is not yet decided whether to print IMs or TDs only.):      There will be textual notes with IMs wherever it seems important to point out that a difference might well be caused by transcriber's error, for although no typist or typesetter added on his/her own whim "straw braces" after "fight shirt" (FW 85:34 at level 9) or substituted "send treats in their times" for "send them Treats" (FW: 92.22 at level 8+T), transcription errors (especially of punctuation) can as well have been made made on missing documents as on surviving ones. Therefore the user who wishes our judgment as to missing documents may display changes postulated on them as "IM"; the user who wishes to know exactly what changes are authorized in the surviving documents may display all unauthorized changes as "TD".
    Matters of textual interest and important facts about the documents ink colors of overlay, unusual locations of drafts on supplementary pages, etc. are discussed in copious "TN"s (textual notes), displayed as endnotes to the printed representation of each Wake page and accessible by hypertext links in the electronic version.
The notation system:

        Boldface designates first-draft text (level 0, in the system of the "draft tables" of The James Joyce Archive, used with a few modifications throughout). Display in red designates text deleted at any revision level (so bolded red designates text inscribed and deleted in the first draft). Normal type designates text which survives at the highest level being displayed. The first draft may thus be "read off" from the bold; the document at the highest level being displayed (including the last, the corrected book) may be read off from whatever is not in red. And the red shows what was present before that highest level, but which was dropped or changed within the selected range.
        Superscripted bracketed numbers enclose changes at a given level after the first draft: "a [1 <long> high 1] perch" (FW: 31.02) shows "high" replacing the first draft's "long" at level 1. Superscripted carets indicate overlay additions within a level: "[3 , faced »feets« to the east, 3]" (FW: 76.11-12) shows ", faced to the east," added as first-degree overlay to a typescript and then "faced" (but not the comma) scratched out and the second-degree overlay "feets" replacing it.3

The specifics are perhaps best listed, with examples:

1) Authorized changes between levels. Note well: Where the first element after the level-indicating bracketed number is in red, that element was present on the level immediately below the level indicated (with one rare exception, for which see "deletion of text new at level" under "Changes within levels").
. . . [x newtext x] . . .
: currente calamo addition: "the [4 relics of the 4] bones" ( FW: 91.05). The phrase "relics of the" is added at level 4, during Joyce's fair copying of the level 3 typescript.
[x newtext x]
: overlay addition: "It was the Lord's [3 own 3] day [3 for damp 3] " (FW: 51.24). Joyce overlays "own" and "for damp" on the level 3 typescript, which is the substrate of the level 3 revisions.
[x <text> x]
: omission: "had not been [1 [4 <very> 4] 1] many" (FW: 41.10-11). Joyce adds "very" in his level 1 copy of the first draft, but drops it at level 4.
[x <oldtext> newtext x]
:substitution: "to ask [1 <if he could> could he 1] [2 <say> tell 2] [1 <what it was> how much 1] o'clock [1 it was 1]" (FW: 35.18-19). Oldtext is omitted during Joyce's copying and is "silently" replaced by newtext (therefore, no overlay carets); the symbols "< . . .> " mean that what they contain is not struck out, but rather that it has not been copied forward. Here, while copying at level 1 Joyce changes "to ask if he could say what it was o'clock" to "to ask could he say how much o'clock it was", and while copying at level 2 replaces "say" with "tell".
[x oldtext newtext x]
: replacement currente calamo: "any luvial mud [4 on to o'er 4] his face" (FW: 86.19). Oldtext on the substrate is copied to the new document, but then struck out and newtext inscribed as Joyce's copying continues. (This is quite rare between levels, but more common within a level.)
[x oldtext newtext x]
:replacement by overlay: "to [3 repeat pianissime 3] a slightly varied version" (FW: 38.30-1); or "with [3 deadly accuracy Anny Oakley deadliness 3] "(FW: 52.01); or "such a [8 wonderful wanderful 8] noyth untirely". (FW: 59.13). This is more common than replacement currente calamo and is, in fact, Joyce's main revision technique. Note that he almost never (I cannot find an unproblematic example) simply strikes text without replacing it: if he did, it would look like these examples without the overlay.
. . . [x <text as of previous level> x] . . . [x text copied at this level x]
:movement between levels: "petties and shouting [4 <whether he was sure of his> 4] name [4 <»names« . . .That would do, «‹> 4] . There were cries . . . " (FW: 87.29); ". . . altar [4 . And a new complexion was put on the matter when to the The mixer, accordingly, was bluntly broached as to whether he was one of those »lucky cocks« for whom the audible - visible gnosible - edible world existed. That he was only too sure of it. Whether he was sure too of his names . . ." (FW: 88. 04-12).  Joyce drops the level 3 passage which, much extended, becomes FW: 88.11-90.33; he then copies it at level 4 where he precedes it with fresh overlay. (Note: often movement between levels is caused by a typist or typesetter misinterpreting Joyce's indexing marks: marked the same, but as TD in both locations.)
2)Authorized changes within levels:
[x {newtext} x]
:initial inscription and deletion: "Was six pounds fifteen [1 {in all}»in round figures«‹ 1] taken [1from off 1] you" (FW82.14-15). This is the rare false start, in which Joyce writes something new as the first element of change at a level and then deletes or replaces it. The special symbols "{. . .}" are needed to show that the element was not present on the previous document, unlike all other first elements which are in red. In the example, note the difference: "from" was present in the first draft, "in all" was not.
[x . . . text . . . x]
:deletion of text new at a level: "[8 . . . the refaced unmansionables of brown gingerdied hue . . . 8]" (FW: 82.26: "gingerdied" added); or " [8 and to league his pagan lot, palm and patte, with a papishee : »For mine qvinnie I thee rape ›››giftake‹‹‹ and bind my hosenband I thee haltar«‹ 8] " (FW: 62.06-9: note "giftake" added as third-level overlay). Note that Joyce strikes out "brown" and "rape" but continues with "gingerdied" currente calamo and "giftake" in overlay.
[x text x]
    :overlay, first degree: "in fealty sworn [9 (my bravor best! my fraur! ) 9]" (FW: 38.33). Note that all overlay carets "travel with" the text they mark: "the [3 overture [9 overthrew overthrewer 9] 3] to the [3 third 3] last [3 day days of [5 TD <pompery> Pompery 5] 3]": the carets around "overthrew" show that it was overlay at level 3, where it replaced the first draft's "overture"; the caret after "pompery" travels back to show that "days of pompery" was the phrase replacing "day", before the TD which capitalized "Pompery" at level 5.
[x . . . »text« . . . x]
:overlay, second degree: "[3 in a burst »loudburst« of poesy [4 , 4] 3]" (FW: 91.03). The "burst" of the first overlay addition is struck out in revision and replaced by "loudburst".
[x . . . ». . . ›››text‹‹‹ . . .« . . . x]
:overlay, third degree: "after which [3 stag luncheon »and a few ones more ›››, flushed with their firestufffostered friendship,‹‹‹ to celebrate yesterday« ‹ 3]" (FW: 42.06-7). After adding "stag luncheon" to follow "after which", Joyce adds to it "and a few ones more to celebrate yesterday", and then inserts ", flushed with their firestufffostered friendship," within that.
[x . . . ». . . ›››. . . »»text«« . . .‹‹‹ . . .« . . . x]
:overlay, fourth degree: "not forgetting [3 a »particularist« prebendary pondering on the Roman question »easter, ›››the tonsure question & Greek uniates»», plunk em,«« ‹‹‹ « ‹ 3]" (FW: 43.12-13). To "Roman easter", replacing "Roman question", Joyce adds first "the tonsure question & Greek uniates" and then "plunk em,". The embeddings occasionally reach to six degrees.
[x . . . text first placed . . . x] . . . [x »text next placed« x]
:movement within a level: "Sordid Sam [8 », the unwashed« 8], haunted always by his ham, [8 »the unwished« , at a word from Israfel the summoner, 8] passed away . . . propelled from [8 {the unwashed} 8] Behind into the [8 great the unwished greatTN1 8] Beyond" (FW: 49.21-5). Joyce overlays "the unwashed" and "the unwished" to precede "Behind" and "Beyond", and moves them (with pencil lines invisible in the Archive) to follow "Sam" and "ham". Note that the second placement is marked as second degree overlay since it is within the same level as and replaces deleted first degree overlay. (This form of revision is very rare.) 
3)Unauthorized differences between levels:
[x TD <oldtext> newtext x]
:transmissional departure: "wore a raffles ticket [5 TD <in> on 5] his hat" (FW50.26). The level 5 typist mistakes Joyce's level 4 "in" for "on".
[x IM <oldtext> newtext x]
:instruction missing: "proclaim him [5' IM <a descendant> offsprout 5'] of vikings" (FW30.08-9). Proofs of the Contact Collection (level 4*) are missing, on which surely Joyce surely instructed for the change we see in the printed Contact Collection.
 [12* . . . 12*]
:the page proofs: The one exception to the marking of IMs is that all changes which must have been made on the missing page proofs are shown as overlay revisions, for user convenience: "[4 . . . [9 , In Custody of the Polis, 9] [9T TD : 9T] 4] [12* Boawwll's [13 alocutionist Alocutionist 13] , [13 deposed Deposed 13] , 12*]" (FW: 72.16). Here the epithet which brings Joyce's total to 111, "Boawwll's alocutionist, deposed," (modified a bit in Joyce's post-publication corrections, level 13), must be an addition made on the page proofs.
4) Further symbols:
[x . . . - x] and [x - . . . x]
: revisions which cross page boundaries: that a revision is not fully contained on a single Wake page is shown by one hyphen preceding the level indicator on the page beyond which it is continued and another after the level indicator on the page on which it is continued: ". . . [1 . . . [2 [3 which what 3] all did - 2] - 1] [page break] [1 - [2 - so [3 that as 3] he was able to add 2] . . . 1]" (FW:54.36-55.01). The level 2 overlay "which all did so that he was able to add" extends across what become pages 54 and 55. Note that this is contained within a level 1 revision which has also begun on page 54 (or previously) and continues on page 55 (or beyond).
. . . õ . . .
:word illegible: " [3 . . . Sycomore Lane [4 <Arrah, Nick, ses she, you've the nock, ses she, with your õ , ses she, ye õ, »says she« > . Fine feelplay . . . 4] . . . 3] " (FW: 95.21). Two words, in a sentence not copied from its initial draft, are enticing but illegible.
. . . ò . . .
:letter, letter sequence or mark of punctuation illegible. Unlike the preceding, this mark may cover more than one letter, because it is far harder than with words to tell how many letters are involved when you can't make them out!: " [3 ›». . . at Multifarnham. Baò----------------. That would do, «‹ 3] ": After the two or three illegible letters which follow "Ba" in the initial draft of what will become the thunderword at FW: 90.31, Joyce puts as placemarkers a line and two part-lines of dashes.
. . . text . . .
:reading not certain: " [8 . . . Bigamy Bob and [8+ <and sould Sin Shanock> his old Shanvocht 8+] . . . . 8] " (FW: 48.03). What is thus marked is not so illegible as to warrant the refusal of a reading, but is far too doubtful to propose with confidence.
[x ±text . . . x]
:insert mark missing: " [5 (commonplace!) 5] [8 ±, since known as Whiddington Wild, 8] his simple . . . ." (FW: 52.10). The "Whiddington Wild" overlay is drafted on level 8 in the top margin with no index mark and no mark in the text. I show it where placed at 8+. A textual note usually gives details.
. . . ¤ . . .
:insert mark present but insert missing: "[3 . . . the Roman¤ Godhelic faix . . . 3]" (FW: 91.35-6). There is an "R" index mark following "Roman" at level 3, but no overlay matches it. As above, this situation will usually be discussed further in a textual note.


Notes
 
 

1 The symbols used are modelled as closely as utility and user-friendliness permit on those used in the 1986 Ulysses of which Hans Walter Gabler was main editor, especially those symbols which designate documents with numbered superscripted brackets  and those which indicate the degree of overlay addition to the text by a system of caret marks (modified from Gabler's system). The most notable departures are that 1) first draft is in boldface, thus, rather than bracketed as zero level, "[0 . . . 0]" , and 2) deletions are shown  in red, thus rather than with pointed brackets, "<. . .>".  (Two specific varieties of deletion, one of which does involve pointed brackets, are discussed below).

2 When IMs are shown, all changes imputed to the missing documents are marked IM, rather than some IM and some TD. That is, no guesses are displayed as to which might be typist's or typesetter's error and which might be Joyce's instruction on those documents. But textual notes often point out that a difference might well be caused by transcriber's error--for although no typist or typesetter added on his/her own whim "straw braces" after "fight shirt" (FW 85:34 at level 9) or substituted "send treats in their times" for "send them Treats" (FW: 92.22 at level 8+T), transcription errors (especially of punctuation) can as well have been made made on missing documents as on surviving ones.

3 "Overlay" means that text is inscribed interlinearly or somewhere else (e.g., a margin, a verso of a preceding page, a supplementary sheet notes designate where, if it is not near by on the document being revised); the point of insertion is (usually) indexed by some symbol or combination of symbols such as caret marks, connecting lines, letters or numbers. If these are missing that fact is marked, as is the presence of such indices without matching overlay (see below).