data <- read.csv("voltage.csv", header = TRUE)    

time <- data[,1]
voltage <- data[,2]
n <- length(time)

lm1 <- lm(log(time) ~ voltage)
summary(lm1)
anova(lm1)

par(mfrow=c(1,2))
plot(lm1$fit, lm1$resid)

lm2 <- lm(log(time) ~ data$GROUP)     # this is the "complete model" ANOVA to test for lack of fit
anova(lm2)
plot(lm2$fit, lm2$resid)