Yes, the Rega RB300 is a pivoted tonearm (as are all of the Rega tonearms). Linear tracking tonearms are very distinctive: they have a base which extends across the back of the turntable, and the cartridge is mounted to an arm that tracks perpendicular to the LP (imagine the cartridge following a straight line from the edge of the LP directly to the center hole of the LP).
There are very few linear tracking arms still made, so virtually every tonearm on the market today is a pivoted design. The design of the pivot itself usually falls into one of two categories: a unipivot (such as the Graham 2.2), or a ball bearing type such as the Regas.
There are very few linear tracking arms still made, so virtually every tonearm on the market today is a pivoted design. The design of the pivot itself usually falls into one of two categories: a unipivot (such as the Graham 2.2), or a ball bearing type such as the Regas.