Stop the confusion!(M1A1 Tank ...)

From: PS, the Preventive Maintenance Monthly | Date: March 1, 2004 | Copyright information

Dear Half-Mast,

I'm confused. How many periscopes, NSN 6650-01-370-5628, are needed for the driver's hatch center position and loader's hatch on my M1A1 tank?

Item 1 on Page B-3 in the old version of TM 9-2350-264-10-2 (Sep 90 w/Ch 17) listed 1 ea as the quantity required required. But when the TM was updated in Apr 03, the quantity required changed to 2.

Do I need only 1 periscope, 1 For each hatch, or two for each ha...