There is an art (and a science) to numerical precision that seems lost in software, writing and conversation. The trick to appropriate precision is understanding accuracy. This all falls under the banner of numeracy.
For example, I just received a confirmation of a cinema booking that gave the time of the film in HH:MM:SS format. The site lists programme times in HH:MM. They normally start trailers within a few minutes of the advertised time. To list seconds is an innumerate and false promise.
I sometimes receive notifications that I can expect a delivery in a 2-hour window such as "between 12:07 and 14:07".
To quote to the minute shows a failure of understanding of what an approximate range is, as well traffic and logistics.
It's a 2-hour window of imprecision. Quoting to the minute shows a deep lack of understanding. Quoting to 5-minute intervals is just about acceptable. To 10- or 15-minute is more appropriate significance. But honestly, in this case, to the hour is just fine.
Received a message telling me to expect a delivery "between 09:50am and 2:45pm". To their credit, they avoided quoting the estimated range to the minute (or to the second!), but the implication of quoting such limits to a precision of 5 minutes is nonsense given that the window of uncertainty is 5 hours.
When developing software systems, understand your domain and understand your users. Your users are human, so go with "between 10am and 3pm" to sound like you know what you're doing.
@kevlin The problem with saying between 10 and 15, is that if they then arrive between 09:50 and 10:00, there will be people who'll complain that they arrived "too early", and if you then instead say between 09:00 and 15:00, then people will complain the window is too wide and "imprecise".
The fake(*) precision is part of the message, that it's specific to your delivery and that you shouldn't bother contacting customer service to get a real time window.
*: see next reply...
@mrotteveel @kevlin Indeed. That 09:50 figure being to the nearest 5 minutes is not, of itself, a problem. It will be calculated on the basis of the courier leaving the depot at time x, and having a number of journey segments of predictable length. So it's the earliest time that it might arrive. The 2 hour, or 5 hour, finger-in-the-air value? Yeah, it's adding that on and keeping the precision that's the problem
The expected arrival curve is nothing like a Bell curve
@bellinghman @kevlin I have worked on transactional emails and push messages that communicate this type of information to users. Communicating time ranges like this, even with the "fake" precision is the easiest to understand for most people. From a business perspective, it also prevents unnecessary calls, and complaints, to customer service.
Being more vague and less specific, even it's mathematically more correct, is not "better", neither for the customer nor the company communicating it.
@mrotteveel @bellinghman My original posting covers that: that is why you communicate 10:00–15:00. Not only is the range more accurate, but you will also receive fewer complaints than 09:50–14:45.
(And yes, there is a small psychological trick in here that is worth knowing, and for that and other reasons it is better.)
Kevlin Henney
Mark Rotteveel
Alan Bellingham