User blog comment:Christian Wilson/Inv. Stacking glitch/@comment-4583259-20111125171200/@comment-4583259-20111125181725

''Well mine is definitly not adding its multiplying i had a stack of 42100 n put it together wit another n it made it 84200 n kept going up times 2! I... (Christian Wilson at 13:10 Nov 25th)''

Yes, it is multiplying by 2, or adding X+X to get 2X. It's the same thing. Any number added to itself is that number multiplied by 2.

You could also call it "exponential", because if you repeat the multiplications by 2 you get exponential growth: 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, 131072, etc.: which are all powers of 2. Your numbers might be a bit different but it basically doubles each time.