Time - ElectronDepot

D Yuniskis · 2009-11-08T06:21:17+00:00

Hi,In keeping with the spirit of posing challenging(interesting?) questions...Expressing (calendar) *time* to the user presentsa dilemma. Most devices that are aware of calendartime also include provisions for *setting* (i.e.,altering!) the time. And, there are few restrictionsas to how and when the user can alter that timesetting!However, in terms of the machine's viewpoint, time is(must be!) a monotonically increasing function. The"time setting" is just an arbitrary parameter establishedfor the convenience of the user -- it bears no relationshipto "real" time.But, when the user expresses a temporal event, hedoes so in *some* context (this will prove to be theessence of this question). Yet, the machine maybe operating in a *different* context -- or, simplyimpervious to the subtlety of the user's viewpoint!For example, if the user schedules an "appointment"for "3:00PM Tuesday", chances are, he *means* "3:00PM"in some absolute sense. OTOH, if it is 2:00PM presentlyand he wants to do something "in about an hour", he*says* "3:00PM" but really intends that to be "60 minutesfrom NOW".The problem lies in the fact that the time associated with"NOW" is always vulnerable to the user (re)setting the(time-of-day) clock! So, if he happens to realize he needsto set the clock forward one hour (Springtime DST processing)NOW has suddenly *become* 3:00PM -- time for that event thathe scheduled for "in about an hour".I've "solved" this problem by never letting the userchange the machine's notion of "current time". Rather,he can determine the *bias* that should be applied tothe time that the machine *reports* to him, but not thetime itself.(this eliminates a whole class of potential problemsthat can occur with the user altering the time settingwantonly -- at least the machine will be sane in howit deals with those temporally ordered events)I log "time changes" (i.e., "bias adjustments") so I cantranslate the "system time" into whatever "local time"was in effect at the time. ...

Time

Nov 08, 2009 24 Replies

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Cesar Rabak 16 years ago

Do the Prius battery have no shelf life related warranty restrictions?

Cesar Rabak GNU/Linux User 52247. Get counted: http://counter.li.org/

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Tauno Voipio 16 years ago

At least the point is moot in the current situation: You have to wait several months, up to half a year for a fresh Prius. Mostly, the delay is caused for waiting for batteries.

Tauno Voipio tauno voipio (at) iki fi (two Priuses in family)

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Mark Borgerson 16 years ago

Yes. That's a good example of a change between relative and absolute terms.

Mark Borgerson

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Steve Allen 16 years ago

Epoch-based interval time is not a solution, at least not until there is international agreement on what is meant by "second". Right now there are two distinctly different definitions required by various statutes.

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Ignacio G. T. 16 years ago

D Yuniskis escribió:

Einstein showed that even that simple assumption is not true.

Some embedded systems must have into account special and / or general relativity issues.

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