{PLdot} 
Vars: Avg1 (0),Avg2 (0),Avg3 (0), pldot (0); 

Avg1 = ((H + L+ C)/3)[1]; 
Avg2 = ((H + L+ C)/3)[2]; 
Avg3 = ((H + L+ C)/3)[3]; 
pldot = (Avg1+Avg2+Avg3)/3; 

Plot1(pldot,"PLdot");