Earlier methods instructed that the carpet nozzle must maintain contact with the surface of the carpet, utilizing the suction, while later instruction manuals recommended the nozzle be slightly above with only the brush establishing contact and improving airflow around the surface being cleaned. For delicate surfaces, the drive belt that spins the brush bar can be detached so that only suction is used. In 1976 with the introduction of the Classic III, a small plastic window was installed in the belt lifter so the belt could be visually inspected as being intact and installed on the turbine driveshaft, however, this feature was only available for a short time, and was removed in 1981 for the Heritage model. When the Heritage II was introduced in 1984, Kirby revised the carpet nozzle by making it slimmer, and in 1987 a Brush Performance Indicator Light was installed in the top of the carpet nozzle. This device consisted of a coiled copper wire wrapped around a magnet, with additional magnets installed in the rotating vibrating brush that created an electrical charge. A small LED bulb would then light up when the brush bar was spinning; if the light appeared to blink or wasn't illuminated, it meant the brush bar wasn't rotating at the desired speed, and that the nozzle needed to be adjusted up or signifying that an inspection of the drive belt was needed. This feature replaced the earlier plastic window on the belt lifter handle. In 1984 with the Heritage II model, the Toe-Touch height adjustment was modified with a custom adjustment feature called "Micro-Matic", which facilitated the ability to incrementally adjust the lowest preset height position, allowing for the carpet nozzle to clean glued down, minimal pile carpets. The feature was no longer offered on models made after 1990, starting with the Generation 3.