Reporting of calBP timescale

[Christopher Ramsey]

I just wanted a bit of feedback. At the moment for calibrated dates OxCal displays calBC, calCE, calBP etc but for modelled dates (and none-radiocarbon) it omits the cal on the assumption that cal means calibrated and so these are shown as BC, CE, BP etc.

This seems to make sense. However, it has been suggested that the BP should always be given as calBP to prevent confusion with 14C BP. This is actually something that I regularly do for other types of plot and actually makes sense in terms of the options settings. In any case the use of this scale assumes the 1950 (derived from radiocarbon) is being used - so there is some logic to this. I would leave BC/AD/CE/BCE as they are for modelled dates.

Would people be happy if I changed OxCal to always show the timescale as calBP rather than BP as suggested - or do people prefer it as it is at the moment.

Best wishes

Christopher

[Fiona Petchey]

Hi Christopher,

I would prefer calBP on the modelled dates as there is quite a bit of confusion in the literature in the Sth Hemisphere.

Fiona

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Dr. Fiona Petchey Director / Associate Professor Radiocarbon Dating Laboratory Te Aka Mātuatua - School of Science Ph: +64 7 8384278 University of Waikato  Hamilton 3240  |  New Zealand

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[MILLARD, ANDREW R.]

Hi Christopher,

 

Could we not have both as options? For modelling work without C14 or  beyond its limits, BP makes more sense than calBP.

 

Best wishes 

Andrew 

-- 

Dr. Andrew Millard 

Associate Professor of Archaeology,

Durham University, UK 

Email: A.R.M...@durham.ac.uk  

Personal page: https://www.dur.ac.uk/archaeology/staff/?id=160 

Scottish Soldiers Project: https://www.dur.ac.uk/scottishsoldiers 

Dunbar 1650 MOOC: https://www.futurelearn.com/courses/battle-of-dunbar-1650 

 

From: 'Fiona Petchey' via OxCal <ox...@googlegroups.com>
Sent: Friday, July 21, 2023 2:36 AM
To: ox...@googlegroups.com
Subject: Re: Reporting of calBP timescale

 

[EXTERNAL EMAIL]

Hi Christopher,

 

I would prefer calBP on the modelled dates as there is quite a bit of confusion in the literature in the Sth Hemisphere.

 

Fiona

 

On 21/07/2023, at 4:05 AM, Christopher Ramsey <christoph...@arch.ox.ac.uk> wrote:

 

I just wanted a bit of feedback.  At the moment for calibrated dates OxCal displays calBC, calCE, calBP etc but for modelled dates (and none-radiocarbon) it omits the cal on the assumption that cal means calibrated and so these are shown as BC, CE, BP etc.

This seems to make sense.  However, it has been suggested that the BP should always be given as calBP to prevent confusion with 14C BP.  This is actually something that I regularly do for other types of plot and actually makes sense in terms of the options settings.  In any case the use of this scale assumes the 1950 (derived from radiocarbon) is being used - so there is some logic to this.  I would leave BC/AD/CE/BCE as they are for modelled dates.

Would people be happy if I changed OxCal to always show the timescale as calBP rather than BP as suggested - or do people prefer it as it is at the moment.

Best wishes

Christopher

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Dr. Fiona Petchey Director / Associate Professor Radiocarbon Dating Laboratory Te Aka Mātuatua - School of Science Ph: +64 7 8384278 University of Waikato  Hamilton 3240  |  New Zealand

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[Bayliss, Alex]

Hi Chris,

 

Is it possible to give the user the option to choose the timescale for modelled chronologies? It is pretty easy to change it to what you want anyway in a graphics program, but I (for example) use cal AD  for modelled ages from a wiggle-match, but AD if I have a model that includes both radiocarbon dates and coins in that period.

 

I agree that BP can cause confusion, but calBP is hardly relevant for a modelled set of luminescence dates in MI5?

 

I think flexibility is the key.

 

Best wishes,

 

Alex

 

 

 

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From: ox...@googlegroups.com <ox...@googlegroups.com> On Behalf Of MILLARD, ANDREW R.
Sent: 21 July 2023 08:12
To: ox...@googlegroups.com
Subject: RE: Reporting of calBP timescale

 

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Te Aka Mātuatua - School of Science

Ph: +64 7 8384278 University of Waikato  Hamilton 3240  |  New Zealand

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[Susanne Lindauer]

Hi Chris,

 

I, too, think that choosing an option depending on context or other data included in the model might be the best solution. In addition I´m also often confronted with the “b2k” that geoscientists love so much and think this could be included as well? I don´t like it, but I think I need to keep an open mind….

 

Best wishes

Susanne

 

Dr. Susanne Lindauer

 

Research Associate

 

 

Curt-Engelhorn-Zentrum Archäometrie gGmbH Büro C4,8 (3.OG) | 68159 Mannheim T:  +49 621 293 3826 www.ceza.de

 

        

 

 

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-----Ursprüngliche Nachricht-----
Von: ox...@googlegroups.com <ox...@googlegroups.com> Im Auftrag von Christopher Ramsey
Gesendet: Donnerstag, 20. Juli 2023 18:06
An: OxCal group <ox...@googlegroups.com>
Betreff: Reporting of calBP timescale

--

[Michael Grant]

This sounds very sensible but what would also be really useful is the option to use a Ka timescale, or at least b2k, given that oxcal is also very useful for modelling non-radiocarbon dates

[Fredrik Hallgren]

Dear Christopher,

I would prefer calBP as it helps avoid confusion.

best / Fredrik

[Christopher Ramsey]

Yes - though BP with OSL carries the potential confusion as to whether it is really before measurement date BP or converted to 1950. For the latter calBP might still make sense in that it ought to be comparable to calibrated radiocarbon. The same for U-Series which, as I understand it, is normally reported relative to 1950.

Christopher

> On 21 Jul 2023, at 08:33, Bayliss, Alex <Alex.B...@HistoricEngland.org.uk> wrote:
>
> Hi Chris,
> Is it possible to give the user the option to choose the timescale for modelled chronologies? It is pretty easy to change it to what you want anyway in a graphics program, but I (for example) use cal AD for modelled ages from a wiggle-match, but AD if I have a model that includes both radiocarbon dates and coins in that period.
> I agree that BP can cause confusion, but calBP is hardly relevant for a modelled set of luminescence dates in MI5?
> I think flexibility is the key.
> Best wishes,
> Alex
>
>

> <image861d38.JPG>

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[Christopher Ramsey]

Thanks for the suggestions. I will think how to implement some of these things.

One option would be to use a, ka, Ma for non-radiocarbon use as recommended in:

https://doi.org/10.1016%2Fj.quageo.2006.07.001

reserving calBP and BP for radiocarbon. Because IntCal is based on summer growth wood - 0 calBP is anyway actually mid 1950 (ie 1950.5) where as a, ka, Ma (and presumably BP used for non-radiocarbon) etc are normally defined relative to the start of 1950 - (ie 1950.0).

Best wishes

Christopher

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[MILLARD, ANDREW R.]

Hi Christopher,

I can't see any mention of ka, etc., in that paper. In any case, a, ka, Ma are simply units of time and still need a reference point to make them expressions of absolute time, whether that is 1950 (e.g., ka cal BP), 2000 (e.g., ka b2k) or the date of measurement or publication.

Best wishes
Andrew
--
Dr. Andrew Millard
Associate Professor of Archaeology,
Durham University, UK
Email: A.R.M...@durham.ac.uk 

-----Original Message-----
From: ox...@googlegroups.com <ox...@googlegroups.com> On Behalf Of Christopher Ramsey
Sent: Friday, July 21, 2023 10:26 AM
To: OxCal group <ox...@googlegroups.com>
Subject: Re: Reporting of calBP timescale

[EXTERNAL EMAIL]

Thanks for the suggestions. I will think how to implement some of these things.

One option would be to use a, ka, Ma for non-radiocarbon use as recommended in:

https://doi.org/10.1016/j.quageo.2006.07.001

[Christopher Ramsey]

Andrew

No - that paper simply recommends not using calBP for non-radiocarbon purposes when it just means BP. The use of Ma and ka as ages is commonly used in geology with present defined as 1950 - eg as in:

https://ngmdb.usgs.gov/Info/NACSN/Code2/code2.html#Article13

If anyone can find any definitive reference as to whether that is mid 1950 or 1950-01-01 as specified (without references) in:

https://en.wikipedia.org/wiki/Before_Present

Note that the issue of year length is discussed in references from:

https://en.wikipedia.org/wiki/Year

In OxCal it was specified that the unit is a_g (as specified in the IUPAP Green and Gold books since 1993) rather than the currently recommended a_t - but fortunately there is almost no difference between these. The important thing is that it is not the a_j.

Of more relevance is the start point for the timescale for ka, calBP etc. The way we use calBP in the calibration curve actually applies to whole years and for the NH data which underlies IntCal this implies mid 1950 - hence 0calBP covering all the period 1950-1951 (ie as an average 1950.5). Dating methods like U-Series are sufficiently good that it almost matters whether an age is relative to 1950.0 or 1950.5.

Best wishes

Christopher

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[Martina Steffen]

Christopher and the forum:

What is the best current convention for the abbreviation of thousands of years in a calibrated radiocarbon date? For example, 10,670 calBP could be written as 10.67 ka calBP or 10.67 cal ka BP or some alternative? The abbreviation of thousands can complicate the reporting of radiocarbon dates.