Website of a professional Clock and Watcher repairman. George's Antique Clocks. Below serial number table is from my book. It is by far the most accurate serial number/date table available for dating a Lenzkirch clock.

Commercial production began about 3rd qtr 1920. Production stopped in 1939 and did not resume until after the war, then stopped for good in 1954 following Bulle's death. A total of about 330,000 clocks were made, apparently all being sequentially numbered. Siemens Drive Monitor V5.5. Without factory or other documentation the above numbers need to be considered a best estimate and used with caution, especially the post war numbers. Source: John Hubby dba Pas-Times 400-Day Clock Specialist; P.O. Box 9543, The Woodlands, TX; AWI BHI NAWCC (Secretary, International 400-Day Clock Chapter #168) E-Mail pastimes@juno.com.