The SMURF system is the Spider-Fan database numbering system which attempts to place every Spider-Man story in a single continuity. It attempts to answer the following question:
How can I read Spider-Man's complete mainstream history in sequence?
The SMURF code is a number between 000.000 and 999.999 which defines the sequence for every Spider-Man story which take place in the default "Universe-616" Marvel continuity.
SMURF codes are assigned according to the following basic rules:
A flashback receives a separate SMURF code only if it flashes back to a separate comic book. A self-contained flashback within the story does not need a dedicated SMURF code. For example, in Amazing Spider-Man #42 there is a flashback at the end which shows events which occurred just prior to the first page.
This is entirely self-contained because it does not refer to any other comic book. The "most natural" reading order would be to read all of ASM #42 in page order. Attempting to read the flashback first would be counter-productive. For this reason, that flashback should not have a separate SMURF code.
A story may have more than one SMURF code if it takes place over an extended period of time such that it does not fit neatly into one sequential slot relative to the other issues. When a story has more than one SMURF code, each SMURF entry should have a "part" (a page, panel, or page/panel range) defined to specify which story fragment is associated with which SMURF code.
SpiderFan uses a "part" syntax which is the same as used by the Marvel Chronology Project except that we drop the "()" braces and remove all spaces. A "part" is either a single page e.g. "6", or a single panel e.g. "4:2", or a range from a starting page or page:panel to an ending page or page:panel such as "4-7", "4:1-4:5", "1-13:2", "1:7-19". In some complex cases you may need to specify multiple fragments separated by a comma "," e.g. "3,4:7-4:9".
A story which has only a single SMURF code entry may (and should) leave the "part" field as empty to indicate that the single SMURF code applies to all pages in the story. This is a "Pages = All & Panels = All" SMURF entry, or a "PAPA SMURF". One issue may have at most one PAPA SMURF.
It is possible that a single numeric SMURF code can be assigned to more than one issue. This is uncommon, but it occurs when a single story incident is re-told multiple times – either exactly repeated, or re-told from a different point of view.