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The missing context in this quote is apparently that you then use a part of your hand after the arm is extended to guage 10° in the sky. Look where you got that quote from, and it probably mention...
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#1: Initial revision
The missing context in this quote is apparently that you then use a part of your hand after the arm is extended to guage 10° in the sky. Look where you got that quote from, and it probably mentions the palm, 4 fingers together, or the like. The point is, this gives you a rough guide how far the sun will appear to move in the sky in an hour. As the quote mentions, ideally you want to measure out 15°.