Quote Originally Posted by zekin View Post
Because a satchel when it is flat it's 40cm long right? , but it actually have two sides, front and back, so, imagine this 40cm of front and back form a 3d shape, then this 3d shape must have 80cm , theoretically 2 x one side and 2 x adjacent side (a rectangle has 4 sides) formed by the back of satchel (40cm) and the front of satchel (another 40cm).

hmm headache.

Am I on right track?
Oh yes I think I can explain with girth

Let's assume L is the longest, L > W > H

Girth = (W+H)*2
see max girth is 60cm because it's satchel's width 30cm x 2. If you take object's Length in consideration, it can work the same way, the max "(L + H) x 2" should be 80.

I believe this is the validation check that you can make sure the box can fit in a satchel or not.