Baird adopted an intermediate film technique where the live material was filmed using a standard film camera mounted on a large cabinet which contained a rapid processing unit and an early flying spot scanner to produce the video output for transmission. The pioneer broadcasts were not, however, preserved on this intermediate film as the nitrate (celluloid) stock was scanned while still wet from the fixer bath and never washed to remove the fixer chemicals. Consequently, the film decomposed very soon after transmission; nothing is known to have survived. No studio or OB programmes from 1936 to 1939 or 1946 to 1947 have survived because there was no means of preserving them. Historical 'firsts' from this era; the world's earliest television crime drama "Telecrime" (1938–39 and 1946) or "Pinwright's Progress" (1946–47, the world's first regular situation comedy), only remain visually as a handful of still photographs. The earliest recording method for television was telerecording, which involved recording the image from a special television monitor onto film with a modified film camera. Early examples made by this method include the first two episodes of "The Quatermass Experiment" (1953), transmitted live while simultaneously telerecorded. The visual quality of the second episode's recording was considered so poor—a fly entered the gap between the camera and monitor at one point—that the remainder of the series was not recorded. Although 2-inch Quadruplex videotape recording technology was utilised in the UK from 1958, this system was expensive and complex; recorded programmes were often erased after broadcast. The vast majority of live programmes were never recorded at all. Videotape was not initially thought to be a permanent archivable medium – its high cost and the potential reuse of the tapes led to the transfer of programme material to film via telerecording whenever sales of overseas screening rights were possible or preservation deemed worthwhile. The recycling of videotapes, coupled with savings made on the storage of the bulky 2" tapes, enabled the BBC to keep costs down. Drama and entertainment output was studio-based and followed the tradition of live theatre. Conventional filmmaking was only gradually introduced from the 1960s. "The Sunday Night Play" (a major event in the 1950s) was performed live in the studio. On Thursday, because telerecording was of insufficient broadcast quality, another live performance followed, the artists returning to perform the play again. Today, most programmes are pre-recorded and it is relatively inexpensive to preserve programming for posterity; even so, the BBC Charter makes no mention of any obligation to retain all of them.