It's not supposed to bend around the head. You put it above your head and adjust the joints to pinpoint the relevant points on your skull, like this:
Attachment 115036
After you've adjusted the meter to the relevant points, you carefully remove it (so the joints of the meter don't change) and put it on a table, then use another meter to measure the distance between the end points of the meter which marked your skull measurements. If you're being very careful and precise, and do several different tries until you keep getting a consistent measurement, I think you should get a fairly accurate result.
Also, I think it's better to use those plastic meters as I pictured previously, rather than the wooden ones, as those in plastic tend to have a bit more rigid joints and don't move around as easily.
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