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Due to the show's long run, the timeline was noticeably slowed. The show was set in May 1976 upon its August 23, 1998 premiere. After twelve episodes of the first season (as well as episode 23, "Grandma's Dead", due to it being aired out of production order), the series transitioned to 1977, where it remained until late in the third season, then the time setting was 1978 until early in the sixth season. The remaining episodes took place in 1979. Hyde had an 18th birthday in 1978, despite dialogue suggesting that he is older than Eric, who turned 17 in episode 2, "Eric's Birthday" (set in 1976). Eric then turned 18 in episode 131, "Magic Bus" in 1978, two years after turning 17. Furthermore, all of the teenage characters are juniors in high school at the beginning of the series (except for Jackie, who is a year younger) and they don't become seniors until Season 5, which they also graduate in the season finale. This, combined with the fact that there were holiday-themed episodes almost every season, indicated a sense of time on That '70s Show that was loose at best.
Season seven uses Hyde's record store for in-jokes aimed at the timeline. In the episode "You Can't Always Get What You Want" the record store opens on Thanksgiving. One of the Led Zeppelin posters on its wall has a famous photograph taken to promote the band's August 1979 concerts at Knebworth. This means that this Thanksgiving has to be in 1979 and so most of the subsequent episodes must take place in 1980. In "It's All Over Now" the record store has a signing for Tom Jones. The fans have copies of the album Close-up, which was released in 1972. In the season finale, Hyde has some records in his hand. The top one is Blondie's Warchild: this was released in 1982.
The year is determined in the last scene of the opening credits, which reveals a close-up of a Wisconsin license plate that reads the names of the creators and the sticker with the two-digit year — in this case, either "76," "77," "78,"or "79," and, in the final episode, "80." The year stickers for Wisconsin plates are issued for the upcoming twelve months (e.g., a sticker for "80" would be issued in 1979). The plate also appears at the end as the production logo for Carsey-Werner, also showing the year.