Tom & all,
Hard and fast rules and measure are good for modelling as was done in the example. Real world centres are messy. There is an ebb and flow to the occupancy measure by time of day and day of week. Centre management are always trying to optimize staff with demand. In Shawn McCarty’s comment he mentions the 85% rule. Allow me to add a range as well as some more absolutes to the discussion.
First if the centre aims for a 75% (could be as low as 70%) to 85% (could be in the low 80% range) then usually the staff have enough work at a rate they can cope with and callers are usually well serviced in the 80% of call being answered within 20 sec. a norm for most customer service. 911 or tech support are different cases and service level. Below that rate, 75% the staff have too much time between calls and can be bored, get distracted and often develop other poor behaviours.
Above the 85% is not hard and fast, but time dependent. For some periods of the day, week, or season, staff and the centre can operate at or above that 85% point. For how long is the better question. In practice, keeping a centre at or above that threshold for more than two weeks usually starts to wear on the staff. This results in turnover (very high cost), absenteeism (high effect on the service level).
Final point is how and when to measure occupancy. Best practice is to do so daily for observational purpose and weekly for tracking and decision purposes. This weekly centre measure will reduce the noise and the variation of the daily and hour fluctuations. And will give a measure that is actionable and not just a model.
Tom, fyi, all of our team use Westbay Traffic Calculators,. Colin and I have used them often in live discussions with clients and presentations. Thank you for this tool.