Robert G recently blogged about the “secret” numbers you can find stamped under the left front foot on many Underwoods. I pointed out that there’s also a mysterious number under the angular nickeled piece that covers the right end of the carriage.

Now Robert has started to collect data on these numbers. The two hidden numbers match in every case so far (though sometimes the initial digit is omitted on the foot). But how do they relate to the machine’s serial number? 

Here are some examples from two machines currently in my possession, both made in January 1925 according to the Database.

 

For some reason, the machine with the higher serial number has lower hidden numbers.