Dear bdavis,

This "finger growing trick" is an illusion. It is a common gimmick used
by hypnotists and other stage-type performers. There are a couple of
variations, such as comparing the lengths of the two forearms or legs,
etc. In another guise, there are "arm strength tests," where you gage
the power of two things by how they affect the strength in your
arm (Google: applied kinesiology, wiki), and this has been used to "prove" the
superiority of all sorts of nonsense. What these demonstrations really
show is how suggestive the human mind is, and our infinite capacity to
fool ourselves.

I congratulate you on taking the steps to actually measure your digits.
You wonderfully exemplify the true spirit of a scientist, someone who is
unwilling to take for granted what someone else tells her, but basis her
view of reality on objective, rational experimentation and observation.
I encourage you to further your exploration of the world with such a
rational, enlightened attitude.

Also, you can try this bodily extension demonstration, which IS genuine:
measure your height when you are standing, and compare that to a
measurement of your height when you are lying down. You'll find that when
you are lying down, you are actually several centimeters "taller" than
when you are standing up. The cause is not mystical at all: it's simply
that your spinal column is compressed due to gravity when you stand up!

I wish you the best, and I hope this post will survive long enough for you
to read it, as there's a chance it might be deleted for being too contrary
to the prevailing mindset of the folks running this site.

Best,

HF

P.S.

For a more objective study regarding how the mind remaps itself in
response to certain stimuli which gives the illusion of a bodily limb
growing longer, please consider the following:

Fickle finger's funny feel: digit illusion modifies touch perception

http://www.findarticles.com/p/articles/mi_m1200/is_5_168/ai_n14895410

http://www.sciencenews.org/articles/20050730/fob5ref.asp