An apparatus for setting a dimension parameter relating to a value of a shock absorber dimension of an extension of a shock absorber of an aircraft landing gear. The apparatus includes a processor configured to identify a respective range of values relating to each of a plurality of operating characteristics under which the shock absorber may operate, and identify a respective probability distribution of values for each of the operating characteristics within the identified ranges. The processor is also configured to perform a generation process for generating a plurality of values of the shock absorber dimension by repeatedly selecting, as input into a computer-implemented model for determining a value of the shock absorber dimension, a value of each of the operating characteristics based on the respective probability distributions, and determining a given value of the shock absorber dimension using the selected values and the computer-implemented model.