[whswhs]

The cost structure is a bit odd. You can take One Arm for -10 points, in effect selling back an arm. But you can't sell back the other arm for -20 points; that gives you No Fine Manipulators, which is -30 points. So you can't, for example, simply sell back both arms and then buy one Extra Arm for a base 10 points, with whatever modifiers apply. Instead you have a somewhat arcane calculation of the price of applying Extra Arm modifiers to the cost of the arms you naturally have.

And that means, for example, that if you are building an octopus, you need to note down both two arms with modifiers, having one point cost, and six Extra Arms, having another point cost. These are all identical arms! But they don't all look identical on the character sheet. So they take up extra space, and the writeup is complicated.