Great question — answering as the UphillTech team:
The real answer is that you learn by feel. So what you do is, start feeding it and if it is a little sticky, dust some flour on it. Conversely, if it is too dry and starts to crack, spritz it with a little bit of water from a spray bottle. Soon you will learn when to make these adjustments.
Full answer by Michael Natkin: https://cooking.stackexchange.com/a/11393 (CC BY-SA 2.5).
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