MATLAB: xcorr/autocorr help

#1
I'm working with a gridded map size(137,137,24) where the 24 is a time stamp. Each hour of a given day contains a grid of information. My goal was to autocorrelate the data through the hours. I selected an (x,y) coordinate and then had it autocorrelate through the hours:

[c,lags] = xcorr(p(x,y,:),10,'coeff');

This returns a 137x137x21 matrix with the 11th layer equaling all ones. So this tells me it's autocorrelating something but what exactly i am unsure.
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My issue is that the data one either side of the 11th layer is identical which makes no sense to me and i don't know which layer the script is using to correlate from (i assume the 1st layer but am unsure). Any information is greatly appreciated.