# Gear bit purpose

Sorry, I just at the beginning of my Turing Tumble. Is there someone who can explain me what is the purpose of the gear bit and gear pieces? I have not understood why a gear bit cannot be substitute with other pieces.
Thank-you
Paolo

Hey everybodyâ€“Correct me if Iâ€™m wrong, please. A single gear bit functions exactly like a blue bit, but gear bits are never used alone. When used in pairs, and with the help of ramps, you can make them into a structure that will reset its value. By that I mean, if the first gear bit in a two bit structure is set to 0, you can have its output feed into the second gear bit which willâ€“because of the red gearâ€“reset the first bit back to 0.

Regarding the blue bits, you cannot organize them to reset. In other words, with a blue bit that is preset to 0, when a ball traverses through it, the bit will become 1, and the only way to set it back to 0 is to drop another ball. If this is not clear, I will be glad to explain further, and if itâ€™s wrong, please (PLEASE) correct me.â€“DonV

DonV is right. The gear bits canâ€™t be substituted for the blue bits because the blue bits change each time a ball passes through them. The only way to find out which way they are pointing is to run a ball through them, but in the process they change direction. So if you need to test the position of a bit but it must return to its original position, you need a gear bit construction with two gear bits and a gear to ensure the position resets after the ball passes through.

A different construction with the gear bits allows you to create a bit that will set to left or right depending on whether a ball enters it from the left or the right. So if is set left beforehand and you want it to stay left, feed the ball in from the left. If you want it to change to the right, feed the ball in from the right. This would not be possible with a blue bit. The blue bit cannot stay/go back to the same way it was when a ball passes through it.

If you are just at the beginning, it should all become clear when you get to the later puzzles which introduce various ways to use the gear bits to complete puzzles that would not work with a blue bit.

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