B737-300 Grid No

for b737-300 some grid locations (Grid No) are associated with Circuit Breaker No.
what does the Grid No mean and how is it used?

I've never really used "grid" from chapter 91.

I looked at my copies of the 737-300/400 and 767-200 chapter 91, "grid" is not mentioned at all.
I'm assuming grid location would be Vertical (letters) and Horizontal (numbers) of each breaker on a particular panel.

From your sheet and one I dug out of a 767 manual.
  
     
     


Each breaker has a specific location on each panel. Maintenance Manuals usually call for breakers to be pulled before a task is started. Breaker location is usually mentioned by Panel, Row, and Number.

The pilot's "Red Tab Book" (Emergency Procedures Book) will mention breaker location in the same way.