d = read.table("exmp11-15.txt",header=TRUE,sep=",",
  colClasses=c("numeric","factor","factor"))
plot(as.vector(d$Brand),d$Power)
for(j in 1:4)
  lines(1:5,d$Power[d$Block==j])
        
fit = aov(Power~Brand+Block,data=d)
summary(fit)
plot(fit)
TukeyHSD(fit,which="Brand")
plot(TukeyHSD(fit,which="Brand"));abline(v=0)