Comparatively, little time passes in the Marvel Universe compared to the real world, owing to the serial nature of storytelling, with the stories of certain issues picking up mere seconds after the conclusion of the previous one, while a whole month has passed by in "real-time". Marvel's major heroes were created in the 1960s, but the amount of time that has passed between then and now within the universe itself has (after a prolonged period of being identified as about 10 years in the mid-to-late 1990s) most recently been identified as 13 years. Consequently, the settings of some events which were contemporary when written have to be updated every few years to "make sense" in this floating timeline. Thus, the events of previous stories are considered to have happened within a certain number of years before the publishing date of the current issue. For example, Spider-Man's high school graduation was published in "Amazing Spider-Man" #28 (September 1965), his college graduation in "Amazing Spider-Man" #185 (October 1978), and his high school reunion in "Marvel Knights Spider-Man" #7 (December 2004). Because of the floating timeline, where stories refer to real-life historic events, these references are later ignored or rewritten to suit current sensibilities; for instance, the origin of Iron Man was changed in a 2004 storyline to refer to the War on Terror in Afghanistan, whereas the original Iron Man stories had referred to the Vietnam War in Vietnam; similarly, The Punisher's backstory has also been changed as well.