Right then.....
I'm on the PA payscale, and have gone as high as I can. Therefore no more annual increments, and I'm on a pay freeze. However,.....
I have currently served 31 years (ish). So my pension is 31/70ths of my "final salary". A year from now my pension will be 32/70ths of my "final salary". Yes, the final salary in question won't have changed, but the proportion of that final salary that makes up my pension will have gone up - hence my pension has increased in value.
Now, going from 31 years qualifying to 32 means an increase of 32/31 (if it is easier for you to understand compare 32/70ths to 31/70ths as a ratio), which is 1.0322, or 3.2%. The year following that, when I go from 32 to 33 years, it will only be an increase of 3.1%. However, if I was younger, and say going from 25 to 26 qualifying years, that would be a 4% rise.
Hopefully I have explained that sufficiently well that it makes sense...