MuttleyI suggest that you decide the number of 800m you want to do. Understand that you actually wish to complete them all. After each 800m take whatever rest/recovery you feel you need before doing the next 800m and so on. If you cannot complete the number of 800m planned or finish feeling knackered or find the time for each 800m varies widely it follows that your recovery or rest was insufficient. Also you may find your first 800m needs to feel slow if you are to complete your last 800m with tired legs.Ideally you want each 800m to take roughly the same time from first to last and when you are finished to be comfortably tired but not fatigued. I would suggest you start with a session of 4 x 800m and get your stats from that session. Say your rest periods were 3,4 and 5 mins you might average that to 4 mins between each 800m for your next session.Depending on your perceived degree of difficulty you might add an additional 800m for your next session or two. Only when your are confident that you will be able to complete each 800m in a consistent time should you shorten your rest/recovery but not by too much as you want your sessions to remain as stable as possible. You should find that your 800m time reduces after a while. The problem with prescribed programs or formulae is that they are not tailored for YOU but for teenagers or elites. Another 51 year old will have different 800m times and/or recovery/rest times than you.Best of luck

Muttley, the rest period shouldn't be relative to pace, but to what you want to achieve - and of course it can change over time as you achieve whatever that is.  It's one of those horrible variable things that you're never quite in control of.  800m intervals are good for VO2max efforts, and reasonable for threshold, and could even be speed endurance, though that might be asking a little much.  Now that I've said that I realise that there are different paces in there...  Anyway, a full recovery is for strength and speed (800 is too long for that really, now I think about it), a medium recovery for threshold, and a short recovery would hold you at or near VO2max.  Of course, the recoveries can be at pace too, so a short standing recovery becomes a longer jogging recovery.  At another extreme, running 800@HMP, with 800@MP for 'recovery' is a great pace session for halves and fulls.A long winded way of saying that your second sentence in your original post was correct, except I'd replace golden mean with golden purpose.