Re: [PSAMP] PSAMP-INFO IE realtiveError

[Andrew Johnson <[e-mail]>]

Hi Thomas

I don't think much has changed.  If I filter out the misunderstandings I
think you get something like this:

Tanja:    What's this fixedError thing for?
Paul:     It's the uncertainty of the measurement expressed as a fixed
          amount of the measured units.
Tanja:    That's a confusing name, let's call it absoluteError.
Everyone: OK.
Tanja:    Why do we even need relativeError then?
Andrew:   I think it might be useful for certain measurement devices.
Tanja:    OK, well keep it if you want.


In conclusion, fixedError is now called absoluteError and we'll keep
relativeError in case it's needed.

For those who followed the thread, does that sound fair?


Cheers

Andrew


On Thu, 2008-08-14 at 15:25 +0200, Thomas Dietz wrote:
> Hi Tanja, Andrew, Paul,
> 
> since the topic seems to be settled now can you please summarize your
> discussion in this thread? I would like to know what to put into an updated
> version of the draft so that it can get published asap.
> 
> Best Regards,
> 
> Thomas
> 
> -- 
> Thomas Dietz                 E-mail: [e-mail]
> NEC Europe Ltd.              Phone:  [phone]
> NEC Laboratories Europe      Fax:    [phone]
> Network Research Division
> Kurfuersten-Anlage 36
> 69115 Heidelberg, Germany    http://www.nw.neclab.eu
> 
> NEC Europe Limited           Registered in England 2832014
> Registered Office: NEC House, 1 Victoria Road, London W3 6BL
> 
> > -----Original Message-----
> > From: [e-mail] [mailto:[e-mail]] On Behalf
> > Of Zseby, Tanja
> > Sent: Donnerstag, 14. August 2008 15:03
> > To: Andrew Johnson
> > Cc: psamp; Juergen Quittek
> > Subject: Re: [PSAMP] PSAMP-INFO IE realtiveError
> > 
> > Hi Andrew,
> > 
> > great. So it seems that after a lot of mice stepping on and off the
> > scale we have a common understanding of the terms :-)
> > So to summarize:
> > - we don't need an offset IE
> > - we definitely include the absoluteError IE
> > - we can also include the relativeError IE (maybe you as authors
> > decide?)
> > 
> > Kind regards
> > Tanja
> > 
> > > -----Original Message-----
> > > From: [e-mail] [mailto:[e-mail]] On
> > Behalf
> > > Of Andrew Johnson
> > > Sent: Thursday, August 14, 2008 12:13 AM
> > > To: Zseby, Tanja
> > > Cc: psamp; Juergen Quittek
> > > Subject: Re: [PSAMP] PSAMP-INFO IE realtiveError
> > >
> > > Hi Tanja
> > >
> > >
> > > On Sat, 2008-08-09 at 01:19 +0200, Zseby, Tanja wrote:
> > > > Hi Andrew,
> > > >
> > > > > -----Original Message-----
> > > > > From: [e-mail] [mailto:[e-mail]] On
> > > > > Behalf Of Andrew Johnson
> > > > > Sent: Friday, August 08, 2008 8:48 PM
> > > > > To: Zseby, Tanja
> > > > > Cc: psamp; Juergen Quittek
> > > > > Subject: Re: [PSAMP] PSAMP-INFO IE realtiveError
> > > > >
> > > > >
> > > > > On Fri, 2008-08-08 at 18:07 +0200, Zseby, Tanja wrote:
> > > > > > Hi Andrew,
> > > > > >
> > > > > > lets first forget about the fixed error and say we agree that
> > we
> > > > need
> > > > > > something like an absolute error that defines the maximum error
> > > > > > that can happen at each measurement (given the real error is
> > > unknown).
> > > > > > Then it was unclear for me why you report this together with a
> > > > > > relative error which provides exactly the same information but
> > > > > > only
> > > > > as
> > > > > > percentage of the measured value. It is only for convenience
> > that
> > > > > > we can report either format.
> > > > > >
> > > > > > relError=abserror/measured value
> > > > > >
> > > > > >
> > > > > > e.g. you can e.g. say: The absolute error is +/- 0.2 kg:
> > > > > > Person:   80.50kg +/- 0.2kg
> > > > > > Mouse:     0.50 kg +/- 0.2kg
> > > > > >
> > > > > > That corresponds to the relative errors:
> > > > > > Person:   0.249 %
> > > > > > Mouse:   40%
> > > > >
> > > > > In the Accuracy Report Interpretation you only provide one
> > accuracy
> > > > for
> > > > > the field, you don't report the accuracy per measurement.  The
> > idea
> > > > > is to provide the margin of error for all measurements of a
> > certain
> > > type.
> > > > >
> > > > > The only use of the error field types that was originally
> > intended
> > > > > was in the Accuracy Report Interpretation, where the error is
> > > scoped
> > > > > to
> > > > the
> > > > > field (and optionally template).  Unless you use a new template
> > per
> > > > > record I'm not sure how you would scope the error value to an
> > > > > individual measurement.
> > > >
> > > > But this is absolutely in-line with the above. You can provide one
> > > > absolute error for all timestamps or all byte measurements (or all
> > > > weight measurements). With this you say what is the maximum error
> > > when
> > > > measuring the timestamp or bytes. This maximum error usually
> > depends
> > > > on the measurement method and therefore the absolute error (= the
> > > > maximum possible error) is usually the same for all of the values
> > > > measured with this method. I think this is exactly the same that
> > you
> > > > want to express, correct?
> > >
> > > Ah I see what you mean now.  In general I think that only one type of
> > > error will be reported at once and that most of the time that will be
> > > an absolute error.
> > >
> > > I think there is still value in providing a way to express a relative
> > > error though.  For example, clocks tend to drift over time so the
> > > larger the time measurement the larger the error, i.e. accurate to
> > > within 1 second per day is 0.0011574%.
> > >
> > > Cheers
> > >
> > > Andrew
> > >
> > >
> > > > >
> > > > >
> > > > > > Or you could say: The relative error is +/- 10 %. Then you get
> > > the
> > > > > > corresponding absolute errors:
> > > > > > Person:   80.50kg +/- 8.05 kg
> > > > > > Mouse:     0.50 kg +/ 0.05 kg
> > > > > >
> > > > > > If this is o.k., the second question would be:  do we need
> > > > > > something like an offset/fixed error ?
> > > > > > e.g. Offset: 0.25
> > > > > > Person (real value):   80.50kg
> > > > > > Person (measured):     80.75kg
> > > > > >
> > > > > > Mouse (real value):   0.50 kg
> > > > > > Mouse (measured):     0.75 kg
> > > > > >
> > > > > > The only thing that might be confusing is if you have an offset
> > > > > > and report it together with a relative error, since the
> > relative
> > > > > > error should still refer to the real value (without offset).
> > But
> > > > > > we
> > > > > probably
> > > > > > do not need the offset value.
> > > > >
> > > > > I don't think we have any need for an offset.
> > > >
> > > > o.k. I agree.
> > > >
> > > > >
> > > > > > Hope this was not even more confusing...
> > > > >
> > > > > I think I understand how you may have misunderstood how the error
> > > > > IEs were intended to be used.  I hope I'm making things
> > clearer...
> > > > > perhaps the draft needs some clarification.
> > > >
> > > > I think we have the same understanding (see above). The
> > absoluteError
> > > > gives the maximum value from which a measured value can differ from
> > > > the real value. The error is usually bound to the measurement
> > method
> > > > or system (i.e. the same for subsequent values).
> > > >
> > > > Kind regards,
> > > > Tanja
> > > >
> > > > >
> > > > > Cheers
> > > > >
> > > > > Andrew
> > > > >
> > > > >
> > > > > > Kind regards
> > > > > > Tanja (starting to see white mice)
> > > > > >
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: Andrew Johnson [mailto:[e-mail]]
> > > > > > > Sent: Friday, August 08, 2008 5:14 PM
> > > > > > > To: Zseby, Tanja
> > > > > > > Cc: Paul Aitken; psamp; Juergen Quittek
> > > > > > > Subject: Re: [PSAMP] PSAMP-INFO IE realtiveError
> > > > > > >
> > > > > > > [SNIP]
> > > > > > > > > >> The intention was to say that the clock is 5 minutes
> > > > > > > > > >> slow,
> > > > > > > > > >> +/-
> > > > > > > 10
> > > > > > > > > >> seconds - so there's both an absolute error and a
> > > > > > > > > >> relative
> > > > > > > error.
> > > > > > > > > >>
> > > > > > > > > >
> > > > > > > > > > NOW I finally understand what you meant by fixedError
> > > > > > > > > > initially
> > > > > > > !!
> > > > > > > > > > This I would not consider as error. Any fixed deviation
> > I
> > > > > > > > > > would
> > > > > > > > > rather
> > > > > > > > > > name "offset"...
> > > > > > > > > > If it is known couldn't you add it to the value and
> > > report
> > > > > the
> > > > > > > > > correct
> > > > > > > > > > time?
> > > > > > > > >
> > > > > > > > > In that case there would be no need to ever report
> > > > > "absoluteError"
> > > > > > > -
> > > > > > > > > because all the original measurements can be corrected
> > > > > > > > > before
> > > > > > being
> > > > > > > > > exported.
> > > > > > > >
> > > > > > > > Maybe for clarification:
> > > > > > > > The absoluteError that I propose is different from what you
> > > > > > > > intended by fixedError. absoluteError is a maximum error
> > that
> > > > you
> > > > > > > > would
> > > > > > expect
> > > > > > > > due to the inaccurate measurement (e.g. the timestamp may
> > > vary
> > > > by
> > > > > > +/-
> > > > > > > 5 ms).
> > > > > > > > The real error that you make during measurements is unknown
> > > > > > > > and can vary. Your fixedError is different. It is a fixed
> > and
> > > > > > > > known offset
> > > > > > > for
> > > > > > > > the measured values, correct?
> > > > > > >
> > > > > > > I think the absoluteError is the same as the originally
> > > > fixedError.
> > > > > > In
> > > > > > > Paul's example above the fixedError was +/- 10 seconds.  I'm
> > > not
> > > > > > > sure how you would communicate the "5 minutes slow" part...
> > > > > > >
> > > > > > > The original idea was fixedError would say this is accurate
> > to
> > > > > > > within
> > > > > > X
> > > > > > > units.  Both the fixed and the absolute error can be used
> > > > together,
> > > > > > but
> > > > > > > you just have to go with the least accurate one.  For
> > example,
> > > > > > > if
> > > > > my
> > > > > > > bathroom scales have a fixed error of 0.25kg and a relative
> > > > > > > error
> > > > > of
> > > > > > > 0.5%, then they can weigh a person very accurate, but are
> > > > > > > rubbish for weighing mice:
> > > > > > >   Person1:   81.50kg +/- 0.4kg
> > > > > > >   Mouse1:     0.25kg +/ 0.25kg
> > > > > > >
> > > > > > > Cheers
> > > > > > >
> > > > > > > Andrew
> > > > > >
> > > >
> > _______________________________________________
> > PSAMP mailing list
> > [e-mail]
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