I opened up the compartment in my Speed Graphic case, and what do I find? I like-new Weston Film meter and instruction manual. My question is wheter a conversion chart exists where I can convert new ASA numbers to the old Weston system. If one exists, how accurate is it?

film speed ratings are a dark art. Kodak started, and ASA continued the "minimum threashold" concept.

Weston, Scheiner, DIN all used a different anchor point to establish a speed.

That said, you can have some fun with this link

http://www.geocities.com/thombell/equivalent.html