Combination Unit Dual Speed The Combination Unit is equipped with two drive shafts which rotate at different speeds. The faster speed (1,725 RPM) reduces mixing time required for small quantities (90 gram or less) of investment. The slower speed (425 RPM) is for all mixing purposes, with or without vacuum. Vacuum Power Mixer Plus Single Speed The Vacuum Power Mixer Plus provides a single drive speed of 425 RPM. This slow speed is ideal for mixing quantities from 5 gram to 1,000 gram of plaster, stone, die material, investment and alginate. Ortho Vacuum Power Mixer Plus Includes the Handy-Holder Bowl Support, 875 mL Vac-U-Mixer (#6615), plastic tubing and connections. Features: Vacuum-invest inlays, crowns and bridges with the Vac-U-Spat. Your patterns are smooth and bubble-free Convenient built-in Vibrator Arm enables user to vibrate mix with or without vacuum Both units are easily installed on wall with the mounting board (included). A #6380 Bench Stand is also available for bench-top mounting 3 Year Warranty (US & Canada only)