By default, I tend to favour a weekly assessment interval for routine exception reporting and associated analysis. Monthly is too long for all except the smallest users (although it may be appropriate for passive top-management reports for users of all sizes) and months are also too inconsistent in terms both both of duration and number of working days.

In some applications, daily analysis may be viable, for example:

• in buildings such as data centres which operate seven days a week and respond rapidly to changing weather conditions; or
• in energy-intensive manufacturing processes.

More frequent near-real-time assessment is sometimes attempted but this brings complications that tend to outweigh the benefits. Firstly, there will be error induced by short-term effects such as transients, lags, latencies, and factors which are not practical to take into account but whose random influences would have cancelled out over a longer time interval. Secondly, the cash values of excess consumptions over a short interval are very small. Thus with too-frequent reporting the user is continually bombarded with trivial alerts which often prove fleeting. Not the best recipe for engagement.

Having said that, where fine-grained data are being collected they can be an invaluable diagnostic aid; but the best reporting tactic is to review performance at, say, a daily or weekly interval and use the real-time record for diagnosis by exception.