Demo project

library(datasets)
data("pressure")

#have a look at data 
str(pressure)

## 'data.frame':    19 obs. of  2 variables:
##  $ temperature: num  0 20 40 60 80 100 120 140 160 180 ...
##  $ pressure   : num  0.0002 0.0012 0.006 0.03 0.09 0.27 0.75 1.85 4.2 8.8 ...

head(pressure)

##   temperature pressure
## 1           0   0.0002
## 2          20   0.0012
## 3          40   0.0060
## 4          60   0.0300
## 5          80   0.0900
## 6         100   0.2700

# mean pressure is:
mean(pressure$pressure)

## [1] 124.3367

# mean temperature is:
mean(pressure$temperature)

## [1] 180

plot(pressure~temperature, data = pressure, type = "l", col = "red")

Conclusion : Temperature and pressure are directly proportional in tempreature range 0 to 200 afterwards it becomes exponentially proportional