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Comment by userbinator | Hacker News Reader

There's another non-intuitive and also inconsistent usage of ranges that I find rather confusing: if you say that a meeting is from 9 to 10, it's one hour long. If you say that you'll be on vacation from January 20 to 21, most people seem to think that means two days.

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That's because hours are announced as points in time, while days are seen as time intervals. The duality intervals/separators is essential to the different ways to understand ranges (specially for range differences).

I once developed a shortcut notation to simplify reasoning about ranges differentiating between "point cero" and "interval between 0 to 1", to make off-by-one errors less likely, but in the end it was functionally equivalent to the popular open/closed interval notations.

If anyone is interested in a notation for this kind of integer ranges, the two different styles in the above example could be represented like this:

   /9..10\  : "short" interval : size 1 (hour)  ==  half-open interval [9..10)
 -|20..21|- :  "long" interval : size 2 (days)  ==  closed interval   [20..21]

Specifying vacation range got me in to few confusing situations, so I have a habit now announcing them as: "I'm on vacation from X to Y, returning to the office on Z"...

1 hour meeting -> meeting start at 9 and is expected to finish when it’s no longer 9 1 day vacation -> vacation start on January 20 and is expected to finish when it’s no longer January 20.

Ultimately, it relies on conventions, but I guess now you can see how this one relies on something which has some consistent pattern.

I thought the proper way to say this is January 20 through 21, but seems like most people don't follow this. Probably because it's often abbreviated as 20-21, which is often used for both cases.

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