Hi,
Yes, the book says the plate thickness on the top left corner of each drawing. When it is written "3 plate" it means 3mm thick plate (most of the plates). "1 plate" means 1mm thick plate (ie CP11), 5 plate is 5mm plate (ie : CP10) and so on. it is not the number of plates you need to cut, it is the thickness
Hope this will help.
Regards.
Sylvain