pressure calculation in lammps

I have used that commands in my input file like
compute totalsperatom all stress/atom
compute globalstress all reduce sum c_totalsperatom[1] c_totalsperatom[2] c_totalsperatom[3] c_totalsperatom[4] c_totalsperatom[5] c_totalsperatom[6]

and then i have printed in log file by themo_style

thermo_style custom c_globalstress[1] c_globalstress[2] c_globalstress[3] c_globalstress[4] c_globalstress[5] c_globalstress[6]

but point is that in the manual stress/atom is in the units of pressure*volume. if i divide above printed log file values with volume for each step i am not getting same as pxx pyy pzz pxy pxz pyz in logfile by thermo_style.

Not only this if i calculate pressure by compute command

compute temperature all temp
compute pres all pressure temperature ke pair bond angle dihedral

Now it is matching with thermo_style custom pressure,

but if i calculate pressure separately like pair,bond,angle,dihedral by using command
compute as below

compute pres1 all pressure temperature ke
compute pres2 all pressure temperature pair
compute pres3 all pressure temperature bond
compute pres4 all pressure temperature angle
compute pres5 all pressure temperature dihedral

Now the sum of all the above values is not matching with the thermo_style custom pressure

can you please clarify what is the reason behind this?