TMK,
With strata living their is always some give and take and the older the building the worse the noise will be. I can hear my neighbour going up a down his stairs. The stairs are solid jarrah in both my place and the rest of the strata. While it is unpleasant and not something I want to hear it would be unreasonable of me to expect him to stop using his stairs while I sleep.
Most noise diary’s should have a date, time or time period, what is actually the noise is. For example if you are putting up with loud foot steps due to noising footwear on hard wood floors, note the date, time or time period and put down that you can clearly hear walking (with heels) on hardwood floors. Put down where you are in your place, note if you have any doors or windows open and if you have music or television going. The more information and detail you give the better chance you have of being taken seriously about your complaint. If the noise is say once or twice a week for a few minutes at a time this may be something that is considered normal everyday living for apartments.
Most local councils have on their website an example of a noise dairy if a neighbour is causing a noise problem.
As for noise readings I have been down this path with my local council about my neighbours loud music and have been basically told unless the police come out and determine the music is excess there is nothing more they can do. Any noise readings I take myself would not be valid in my complaint. I am not sure (depending on your state) what the police, council or strata complaint board (depending on your state) view would be and worth checking out.
Hope this helps