# Centroid from calculated root locus is different to the one from MATLAB

Hi all hope someone can help me here.

My problem involves the transfer function

 G(s)=(s+32.8)/((s+2.8)(s+5)(s+27.8) )


As far as im concerned the centroid is calculated using

σ_a= (Ʃpoles - Ʃzeros) / (# of poles - # of zeros)


From my calculations

σ_a=((-2.8+-5+-27.8)-(-32.8))/(3-1)=-1.4


However when i input the following code into MATLAB the solution from the graph shown the centroid will be -1.55

s=tf('s');
G=(s+32.8)/((s+2.8)*(s+5)*(s+27.8));
rlocus(G)


Im not 100% whats the issue but if im doing something wrong could someone please correct me and help me understand.