Was this style of hot box detector unique to Espee ??? I never saw them along other RR's. Upon detecting a hot box, the detector would begin counting axles to the end of the train, then display an axle count in the readout. I believe the 3 lights on top were for multiple hot box detections. This type of hot box detector, with a requirement for rear end crew to observe it, was the reason some Espee lines, including Donner Pass, used cabooses much longer than other lines & RR's. I recall during the floods of 1986, when Feather River Cyn washed out, EwePee detours over Donner were using C&NW & MP cabeese to satisfy Espee's requirement for rear end crew.