The Dual Sanitronic 50 was the first Kirby to have a DUAL speed motor. Low speed for vacuuming floors and High speed when using attachments with the hose. All Kirby's since the D50 have 2 speed motors except the Diamond edition which has 4 speeds. 2 speeds in floor mode and 2 different speeds when in hose mode and selectable with a lighted toggle switch in the rear near the power switch. The Diamond was the only Kirby to have 4 speeds.