In the past 10 months collecting serial numbers has been my focus.
It provides essential background for this site.
Previously undetected gaps in the consecutive M42 serial numbers appear in the 1970's when 6x7 (120 format) lenses commenced and started to share the same SN sequence.
Data observed now supports useful Performance and Production summaries for groups of lenses and enhances individual lens data.
It is systematically replacing "guesstimations" from indirect methods used by others by producing new results and fresh insights.
New group summaries will now be added to this site as the top level of reference for lens groups.
Tele-Takumar, Takumar-Zooms and Auto-Takumar summaries are first.
Building the highest levels of detail on individual lens pages has been delayed, necessarily.
PS. (Questions are welcome.)