It takes fourteen nickles to register a keypress. The key starts to move at eight nickles, and sinks a bit lower with each additional nickel until at 14 it clicks, registers, and bottoms out. Every once in a while it only takes 13 nickels.
This is not a new board -- I think I pounded on it for a year before moving on -- but I measured four different keys this evening, three of them very lightly used.