When it is desired, in the case of a Pension Fund granting pensions based on salary, to calculate the value of the prospective pensions, it is necessary to frame a scale of average salaries at successive ages, so as to give the means of estimating what salaries the present contributing members of the Fund will on the average be receiving up to the time of retirement. The scale is also necessary for the purpose of calculating the values of future contributions and returns of contributions.