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Razors made in USA often left the factory with serial numbers or date codes, which can be used to establish their manufacturing dates.
During certain periods some or all models were unmarked.
So razors made from 1930-49 can be difficult to date precisely.
However, blades made in those years were stamped with a date code: A for 1930, B for 1931, etc., plus 1-4 for the year quarter. In 1950 this system was expanded to include razors, too (see below).
Therefore, a tree with all tips having the same date and no further date information on internal nodes will not able to estimate absolute dates.
LSD: LEAST-SQUARES METHODS TO ESTIMATE RATES AND DATES FROM SERIAL PHYLOGENIES - v0.3beta by Thu-Hien TO If you use this software, please cite: “ Fast dating using least-squares criteria and algorithms”, T-H. If the input date is provided, the program estimates will the absolute dates.
If your data has the reverse order, the simplest way is to take the negation of the input date, and take the negation again of the output date to obtain your expected results. If it's not provided then the program estimates the relative dates by assuming all tips have the same date (1 by default), and the root has date 0 by default.
New Improved (1921-1929, including Bostonian, Big Fellow, etc.)| "O" was not used as a serial number prefix. May launch of New Improved razor with new serial number format, starting with 1A.
The Old Type continues as "Brownie" and various other sets, but without serial numbers. In 1930 Gillette stopped using serial numbers on razors.