IIRC
If you were on acting rank, you accrued additional pension at one third for each year in the acting rank. Thus after 3 years acting, you got the full pension for that rank for your years of service. However, if you had been substantive for two years you got the full rate. (it didnt happen often as you invariably had to waive/defer an option when promoted if you had less than 3 years to do in the new rankl).
Health warning - this was several years ago!!!
F.O.D