My family had an old Family Tree For the name of Kleinman, It had numbers and letters that I don't know where they came from can anyone explain them and were came from :
 
18.2A,  40-8g,  9/77,  
Jerry Kleinman
Jerry2000K@...

Before computers helped us organize our genealogical information, there were a variety of numbering systems. I have a couple of old articles in my files from those days. 

But, since we live in the age of information technology, I looked on the internet and found this Wikipedia article on genealogical numbering systems.  Perhaps it will help:
https://en.wikipedia.org/wiki/Genealogical_numbering_systems

Note that there were many different methods.  You will have to figure out which one your tree uses.

Peggy Mosinger Freedman
Atlanta, GA