Need Mattress measurements 2003 Star Craft 21rb

I am confused by what the 1/3 fold means. Sorry but i am new to this style camper.

How do you like your 03? I just bought mine from a repo lot and got a killer deal in my opinion. Inside is like new. I found some water damage on the door side...underneath the camper behind the rear wheel. Looks like where water would hit as you drive down the road from flying off the wheel. Not sure how to repair yet.