Vibroplex Serial Numbers per Year
John Elwood, WW7P, did a heroic job of determing the age of Vibroplex keys by serial number. One place to find his document is on the Vibroplex site here.
Using WW7P's data, I built a spreadsheet and calculated how many serial numbers were used in each year from 1905 to 1999 and then I graphed it.
I'm not entirely sure that this means anything, but the peaks for the World Wars and the trough for the Great Depression are pretty obvious.
The image is linked to a full-size version of the graph.
