INQUA Working Group on Data-Handling Methods

Newsletter 11: January 1994

RADIOCARBON CALIBRATION NEWS

Since the release of the updated version of the radiocarbon calibration program CALIB (Stuiver and Reimer, 1986; Stuiver and Reimer, 1993), I have fielded numerous questions about calibrating radiocarbon ages, some of which have been easy to answer and some of which have prompted revisions of program details. In the following paragraphs I have sketched answers to a few frequently asked questions about CALIB. Also there are some announcements concerning minor revisions to the DOS version, availability of a test version for the MAC, and a French translation of the CALIB manual.

Question 1: Why don't the sample numbers scroll on the Sample Selection Menu?
Answer: Only the sample ID's scroll to allow sample selection with a single keystroke.

Question 2: Why are the results for only the last sample saved to file when sample identifications are long?
Answer: If sample ID's are not unique, then the CALIB output file is overwritten by the last sample with that ID. Since only the first 8 characters can be used in making up the file name, long sample ID's that differ only in the ninth and tenth character do not generate unique file names.

Question 3: How can I save CALIB plots to import into other programs?
Answer: A utility called CAPTURE.COM, which comes with Microsoft WORD 5.0, can be used in place of the DOS GRAPHICS command. After a plot is finished you can press Shift-Print Screen and the plot will be stored in a format that WORD can import. Other programs may come with similar utilities, so check your wordprocessor or graphics software manual. [WordPerfect has a utility called GRAB.COM which is similar, Ed.]

Question 4: If a laboratory does not supply a lab error multiplier or give an estimate of the added variance to use with their results, what should one use for increasing the error beyond the counting statistics?
Answer: It is nearly impossible to make generalized recommendations for increasing the error in a radiocarbon age beyond that of the counting statistics when the necessary data is not supplied by the laboratory. We refer the user to an interlaboratory comparison (Scott et al.,1992a) which tabulates average laboratory error multipliers (there designated as internal error multipliers) by counting technique and quoted error range. However, use of such an average will reduce precision for the best labs and increase precision for the worst labs. A further intercomparison exercise is being undertaken (Scott et al, 1992b).

In suggesting values for additional variance (f²) in the CALIB User's Guide Rev 3.0.3, we misquoted Clark (1975) as recommending values of f= 50 and 60 years for radiocarbon dates of less than 2700 years and greater than 2700 years, respectively.

From analysis of variance of replicate measurements on treerings in a number of pre-1975 laboratories, Clark recommended increasing the standard error to 50 years and 95 years for radiocarbon dates less than and greater than 2700 years BP, respectively. However, for many radiocarbon dates in the literature, the quoted standard error is already larger than Clark's recommendation, especially for radiocarbon dates on samples older than the 6000 yr wood used in the study. The added variance option can be used by calculating the f value from

where _s is the quoted standard error and _t is the total error.

Of course, _t / _s equals the error multiplier which can be entered directly.

Announcements

Gremlins fixed in CALIB 3.0.3A are:

1. If the cal range changed from BC to AD or if the one range was AD and the two BC, the labels AD or BC were not changed in the printout except in the summary. The ranges were correct on the plots.
2. If using the additional sample variance option the program asks the user to enter the variance f-squared, but the user should really input the value for f in years. (see the Question 4 above for a change in recommended f values)
3. If only the cal BP print option is used, the labels 1 and 2 do not appear on the printout of the ranges.
4. In the manual in Table 1 the charges on the carbonate and bicarbonate ions should all be negative instead of positive.

• MacCalib -- contains information about the current MAC test version of CALIB including bug reports and specific directions for obtaining a test copy
• DOSCalib -- contains information about the current DOS version of CALIB including how to uncompress the program and bug reports
• CALIB3A.EXE -- this is the compressed DOS CALIB program (rev. 3.0.3A) and necessary files
• CALIB_FR.EXE -- this compressed file contains the French version of the CALIB manual in WORD format and in RTF format translated by Phillipe Fortin of The Centre de Datation de le Radiocarbone; Universite Claude Bernard Lyon 1; Centre des Sciences et de la Terra U.R.A. CNRS 11; 43, Bd du 11 Novembre 1918; Batiment 217; 69622 Villeurbanne Cedex; France.

CALIB users are urged to communicate any problems or questions since user input is extremely valuable to keep the program viable. I can be reached at the address at the head of this article.

References.

Clark, R.M., 1975, A calibration curve for radiocarbon dates: Antiquity, v XLIX, p 251-266.

Scott, E.M., Cook, G.T., Harkness, D.D., Miller, B.F., and Baxter, M.S., 1992a, Further analysis of the international intercomparison study (ICS), Radiocarbon, 34, 520-527.

Scott, E.M., Harkness, D.D., Miller, B.F., Cook, G.T., and Baxter, M.S., 1992b, Announcement of a further international intercomparison exercise, Radiocarbon, 34, 520- 527.

Stuiver, M., and Reimer, P.J., 1986, A computer program for radiocarbon age calibration, Radiocarbon, 28, 1022-1030.

Stuiver, M., and Reimer, P.J., 1993, Extended 14C database and revised CALIB radiocarbon calibration program, Radiocarbon, 35, 215-230.