began offering 24-hour programming on weekends in September 1981—may have once stemmed from HBO's pre-mid-2000s availability on analog cable tiers (whereas its multiplex channels generally require a digital cable subscription or at least scrambling), and, because of controversy surrounding daytime showings of R-rated films that began being scheduled on competing premium services as early as 1980, remained in place well after the V-chip became standard in newer television sets. From April 1979 to April 1986, rating bumpers preceding HBO telecasts of R-rated films included a special disclaimer indicating to viewers that the movie would air exclusively during the designated watershed period (“Home Box Office/HBO will show this feature only at night"). The watershed policy was extended to cover TV-MA-rated programs when the TV Parental Guidelines were implemented industry-wide on January 1, 1997, although HBO had already been withholding airing original programs incorporating mature content that would now qualify for a TV-MA rating outside the watershed period. , HBO employs a fairly fluid enforcement of the watershed policy, varying based on the content scheduled to air on its main channel during each individual programming day. The policy began to be weakened in January 2010, when the main HBO channel started allowing original series, movies and documentaries given a TV-MA rating for strong profanity and/or non-graphic violence to air during the daytime on Saturdays and Sundays; in January 2012, HBO began offering occasional Sunday daytime airings of R-rated films within its weekly encore showing of the Saturday movie premiere (airing as early as 4:00 p.m. ET/PT, depending on the previous night's scheduled premiere film, that film's length, and the Sunday night block of HBO original series that usually follows the rebroadcast); by 2017, afternoon R-rated movie airings (which occasionally have been shown as early as 2:00 p.m. ET/PT since then) were permitted in random afternoon timeslots any day of the week on the main channel at the network's discretion. Most of the six HBO thematic multiplex channels—except for HBO Family, which prohibits programming containing either equivalent rating by effect of the channel's target audience and format—air TV-MA and R-rated programming during morning and afternoon time periods. HBO also does not typically allow most NC-17 rated films to be aired on the primary channel or its multiplex channels. HBO pioneered the free preview concept—now a standard promotional tool in the pay television industry—in 1973, as a marketing strategy allowing participating television providers to