Grado Reference3The Master3 and Reference3 models use a five piece OTL cantilever technology achieving an additional 5% tip mass reduction over the Platinum3 and Sonata3 models. The coils are wound with ultra high purity long crystal (UHPLC) oxygen free copper wire. The Master3 model is mounted with Grado's specially designed nude elliptical diamond, and the Reference3 model uses Grado's true ellipsoid design diamond. These cartridges are individually calibrated.