While looking for something else, I found the answer to this question in the Owners Manual for my '51. For some reason, my dipstick only has the full marking, not the add, but it's pretty specific on what I need.

http://pic20.picturetrail.com/VOL1373/13685773/24611517/412972536.jpg
http://pic20.picturetrail.com/VOL1373/13685773/24611517/412972537.jpg


"When I rest, I rust"
1951 3100 5 window w/ '56 235