“Nail Growth: A Twenty-Year Study”, 1963-04 (; backlinks):
Growth of my left thumbnail, measured month by month for a second decade, again revealed no substantial seasonal changes.
The average rate of growth was 0.123 millimeters daily at the age of 32, 0.111 at the age of 42, and 0.105 at the age of 52. A sharp decline began at the age of 49, and seems to be continuing.
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