sentences:  GPS speed measurement is presently only on Coxmate SCT and SX units.Before the development of the Cox Box by Nielsen-Kellerman, a megaphone strapped to the head of the coxswain was used to make the coxswain easier to hear, and the coxswain used an analog stop watch and rate watch - quite a handful when also trying to steer a 60' long racing shell!The use of a system with multiple speakers also became much more important when racing eight construction switched to sealed bulkhead sections to ensure the boat would remain safely buoyant even when damaged.