- 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