You should be cautious with window glass dating.  In my experience with two
particular formulas Moir 1983 and Ball 1984, I have recieved different dates.
The descrepency is often as large as 60 years.  The Ball formula was suppose to
account for regional variation and is specific to the Ohio Valley and as I
understand Moir's formula  was more specific the West.  However, I recieved
dates more conducive to the historical documentation with the Moir formula,
although my sites are in the Ohio Valley region.  I think that there is much
more variation in contemporaneous windows than the formulas account for.  For
example there is variation of thickness within a single window, not to mention
the changes that may occur in a single window over time.  Has anyone looked at
this dating technique in more depth?
 
M. Jay Stottman
University of Kentucky