I just obtained a size 16 Waltham Vanguard circa 1926 with an AWC Co. Toronto case. The case is a Fortune and I am attempting to determine the crystal size. I haven't had any luck finding tables anywhere. The case serial number is 3911141. If I am measuring it accurately, I make the crystal size to be 20 13/16 or 46.9 mm. Does that sound right? Many thanks.