For each group (say 50 groups), for each field (6 fields), for each modem in each group (2500 down to 4 or 5), collect the min, max, mean, and total. Problem is, even summarising 1 field for a 500 modem group is taking a long time (i.e. a second or more).

I'm obviously just doing something stupid. Every single summary page is doing the same work for the same groups in basically no time at all. Something in my attempt to make it faster when dealing with all groups has wound up making it achingly slower.

Bah. It's the weekend, and this is just an extra feature. I think I'll call the week done and do something else for an hour or two before I head off to bed.