Archive - Originally posted on "The Horse's Mouth" - 2005-01-20 03:27:52 - Graham Ellis
Updated - see end of story
REAL coffee. Mmmmmm. Ever since we started running courses here, we've provided customers with superb coffee. Grind the beans as required, brew the coffee with freshly heated pure water and supply a choice of sugars and sweeteners for those who want such things.
Our first coffee machine had a water capacity enough to make 4 mugs of coffee. Beans had to be replenished every 10 mugs or so, and the coffee grounds cleared out about once in every 7. The drip tray needed to be emptied every 12.
Ever come across MTBF - "Mean Time Between Failure" calculations? You take the reciprocal of the sum of the reciprocals of each component failure frequency to calculate your overall failure frequency. Of in our example:
This coffee machine needed servicing more frequently than every two mugs
Our current coffee machine is a commercial machine "That looks like it's suitable for a small but classy cafe" said my son Chris when he visited last weekend and he's right - it came with a table showing numbers of cups of coffee served daily, and prices we could charge, to make certain amounts of money. That bit's irellevant to us since we don't charge customers for coffee - it's free and available whenever it's wanted - but it just shows you.
The capacities of the new machine are much higher, but perhaps not as high as you might think. But that give us a new opportunity. It's called "preventitive maintainance" in the jargon of this article and it means that we can service the coffee machine overnight, and between coffee breaks, and be reassured that it's not going to be forever demanding attention.
Updated with the opening of our new training centre at Well House Manor .... We've installed a new coffee machine that's plumbed in to the mains, that has its own drain, and dumps its grounds into an enormous bin. The coffee hoppers are large too so we're a step further improved!
But the MTBF calculation is an excellent example, and so I've written another example - this time for use on our Ruby course which shows how operator overloading can be done in that language. The source code of the example is available on line, of course!