Have I shrunk?

I've been 5 ft 10 in since I was 14 -- or I've assumed I've been that tall. I realized that I haven't been measured for maybe 15 years. When I go to the doctor's office, they weigh me (usually) but they just ask me how tall I am... even though they use that scale with the height measurement thingy on it.

So I measured myself today, old-fashioned-style. I drew a pencil mark on the edge of the bathroom door (so I could stand on the flat tile floor rather than on carpeting). Then I used two different tape measures and a ruler to see how tall I am.

5'7" (weight-loss measuring tape)
5' 8 + 1/2" (sewing measuring tape)
5'11" (ruler)
5' 9 + 3/8" (hardware store tape measure)

Wha?? Next time I go to the doctor, I'm having them measure me!