how to use fix ave/chunk command output stress

I want to divide the simulation area into different layers and measure the stress of each layer, but when I use the following command, it is not clear whether the one measured by the fix ave / chunk is the stress of one atom or the sum of the stress of the layer.
do you have any suggestions about this?

compute stress c7h16 chunk/atom bin/1d z lower 2
compute C6 c7h16 stress/atom NULL
compute V2 c7h16 voronoi/atom
fix 12 c7h16 ave/chunk 1 1 1 stress c_C6[4] c_C6[5] c_C6[6] c_V2[1] file stress1 ave running

From the “Description” of the fix ave/chunk command:

Use one or more per-atom vectors as inputs every few timesteps, sum the values over the atoms in each chunk at each timestep, then average the per-chunk values over longer timescales.

I think that is pretty clear and specific.