Editing VHS (section)

==== Tracking adjustment and index marking ====
Another linear [[control track|''control'' track]] at the tape's lower edge holds pulses that mark the beginning of every frame of video; these are used to fine-tune the tape speed during playback, so that the high speed rotating heads remained exactly on their helical tracks rather than somewhere between two adjacent tracks (known as "[[video tape tracking|tracking]]"). Since good tracking depends on precise distances between the rotating drum and the fixed control/audio head reading the linear tracks, which usually varies by a couple of micrometers between machines due to manufacturing tolerances, most VCRs offer tracking adjustment, either manual or automatic, to correct such mismatches.

The control track is also used to hold ''index marks'', which were normally written at the beginning of each recording session, and can be found using the VCR's ''index search'' function: this will fast-wind forward or backward to the ''n''th specified index mark, and resume playback from there. At times, higher-end VCRs provided functions for the user to manually add and remove these marks.<ref>{{cite web|url=http://www.crutchfield.com/S-PFiOFC1Dt8s/learn/learningcenter/home/vcr_glossary.html|title=VCRs Glossary|author=Loren Barstow|work=Crutchfield|access-date=2014-07-30|archive-date=2014-08-12|archive-url=https://web.archive.org/web/20140812193000/http://www.crutchfield.com/S-PFiOFC1Dt8s/learn/learningcenter/home/vcr_glossary.html|url-status=dead}}</ref><ref>[http://www.retrevo.com/support/JVC-HR-S7300U-VCRs-manual/id/318ag718/t/2/ JVC HR-S7300 manual] {{Webarchive|url=https://web.archive.org/web/20140810142541/http://www.retrevo.com/support/JVC-HR-S7300U-VCRs-manual/id/318ag718/t/2/ |date=2014-08-10 }}: features list: ''"..., Index Search, Manual Index Mark/Erase ..."''</ref>

By the late 1990s, some high-end VCRs offered more sophisticated indexing. For example, Panasonic's Tape Library system assigned an ID number to each cassette, and logged recording information (channel, date, time and optional program title entered by the user) both on the cassette and in the VCR's memory for up to 900 recordings (600 with titles).<ref>[https://archive.today/20120729233622/http://www.elektroda.pl/rtvforum/instrukcjeobslugi?id=2176 Panasonic Video Cassette Recorder NV-HS960 Series Operating Instructions], VQT8880, Matsushita Electric Industrial Co., Ltd.</ref>