The value of L/360 has been empirically determined to be a reasonable amount of deflection in horizontal structural members. This would be one inch (1") for every thirty feet (30'). Read about this history below.
Originally published June 1964
W.G. Plewes and G.K. Garden
Mechanics of Bending — Boston University
Here you will find a collection of material, ranging from technical data to white papers to theory, which has influenced my thinking.