The two photocells are linked to the Tree: the Pre-Stage, and the Stage lights. When the car inches forward and blocks the first photocell, the Pre-Stage light comes on, indicating that the driver is close to the starting line. Most tracks have a rollout, or distance between the Pre-Stage and Stage beams of 6-8.
Batten disease is named after the British pediatrician Frederick Batten, who first described it in 1903. Also known as Spielmeyer-Vogt-SjÃ¶gren-Batten disease, it is the most common form of a group of disorders called neuronal ceroid lipofuscinosis (or NCLs).
The disease is named for the English physician Waren Tay and New York neurologist Bernard (Barney) Sachs who made key early contributions to the rocognition of this disease. In 1881 Tay described an infant he had seen with progressive neurological impairment and the cherry-red spots in the retina characteristic of TSD.