Turntable anti-skating is a feature used in phonograph turntables to prevent skating of the tonearm. This turntable had a sensor arm that was built next to the tonearm. The top plinth sees mountings for the main bearing and tonearm. An SME tonearm was the usual choice for the audiophile. The tonearm is likewise oriented vertically and has a stylus on each side. To prevent this, an appropriately-sized opposing force (a rotational torque) is applied at the tonearm. Although Keel upgrade is possible for Akito tonearm but not recommended due to collar limitation. It was a compound that virtually eliminated feedback, thus preventing resonance from reaching the tonearm. Recent products include the SME V tonearm, and extremely expensive (and consequently relatively rare) decks. Another problem arises because of the geometry of the tonearm. The tonearm and plastic dust cover hinges remain the same. The SL-120 came without a tonearm section. It was followed by a more advanced version of the tonearm. The Pro TT-2 soon followed with a slightly different tonearm. The tonearm was different to the previous models as it was made from titanium.