Ridiculously messed up wingspan?

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Hey everyone. I found a tape measure, and I thought I'd decided to measure myself again.

So, I leaned against the wall with both hands as outstretched and parallel to the ground as possible. I had the fingertips of one hand against the corner of a wall, and I marked the other one with a pencil.
The mark was at a little less than 5ft4 or 162cm.
I measured again a few times, and I kept getting the same result, if not smaller.

Did I measure wrong? Or is my wingspan just an outlier in the negative?

I've been up for over a day, and my back is really tight, so would that be a factor? Probably not enough to make an 8cm deficit from the norm.

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I think it'd be called a t-rex index lol.
I actually think I have above average shoulders.
Welp, at least I don't even have to think about LLing over 180cm in the future 

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Welp, turns out I'm an idiot.

I read a post somewhere saying measuring wingspan by yourself is tricky and that laying down with arms outstretched is a good way.

This made me realized that I was measuring with a protracted shoulder blade because my back was facing away from the wall.

Remeasure laying on ground: 5'6~ 168cm