• Find the average RTD of each inspection as y using the following:

y = Sum of non-empty RTD (except SH1 and SH2) for each inspection / Number of non-empty RTD (except SH1 and SH2) for each inspection


  • Find mileage of each inspection as x using the following:


x = Odometer difference between each inspection’s fitment odometer reading and last inspection odometer reading.


  • With the list of x, y values, find the gradient, m, where n = number of inspections


m = (sum(x*y) - sum(x)*sum(y)/n) / (sum(x^2) - sum(x)^2/n)


  • With the list of x, y values, find the intercept, c:


 c = sum(y)/n – m*(sum(x)/n)


  • With the intercept, find the estimated life km using the following: 


Estimated life km  = (3 – c)/m