It is probably significantly greater than the mean variation within a group. For example, if the variations within a group were only about 1 degree, then finding a difference of 7 degrees between the groups would be significant. I haven't read the article but I'm assuming they got a bunch of people to read from the displays and they measured the distance and angle they held it at. And actually, considering that there's only a 90 degree difference between holding it flat and holding it vertical, 7 degrees does seem like quite a bit. I wonder what the difference was?
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