Henley: A piston arm is a special kind of arm that can extend and retract.
Anataeus (Student): And presumably there are instructions that control the piston?
Henley: That’s right. I’ll demonstrate.

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Anataeus (Student): I see. Piston arms can reach areas you can’t with a normal arm. 
Henley: That’s what makes them so useful! They cost a little more than regular arms, though.
Anataeus (Student): And I can use the reset instruction to make an arm return to its initial state from wherever it is. That’s convenient.
Henley: Just remember the reset instruction takes the same amount of time it would take to issue those individual instructions.
Anataeus (Student): Well, yes, of course it will.
Henley: Of course.