ArArCALC  |  Help Contents  |  Full Text    

ArArCALC Help Library
First  |  Previous  |  Next  |  Last    

1.4.6  Your First Calculations

Let's assume that ArArCALC is already running (see also: How to start ArArCALC from Excel) and that you have already set your own Project names, Irradiation Parameters and Preferences (see also: Managing Irradiations and Projects, Setting the Preferences). Now you are ready to do your first calculation.

Age and Flux Monitor Samples

Open a raw intensities data file by selecting the File # Open Datafile # Raw Intensity Data menu item.

This will give you the following Open DataFile dialogbox. You can set the default file location for these type of data files in the Preferences dialogbox (see: Setting the Preferences) to speed up your file search. Now scroll, select and Open your data file.

When you open your data file, ArArCALC will show you three dialogboxes in sequence. In the first dialogbox, you have to select an Input Filter. However, you can surpass this dialogbox by unchecking the Choose Input Filter when ... checkbox in the Preferences (see: Setting the Preferences) or by checking the Do not show this dialogbox ... checkbox in the dialogbox shown below. You can use the latter option when you always open your data files with the same input filter.

In the second dialogbox, you have to set the Sample Type and give an Experiment Name (See also: File Name Conventions, Sample Type and Experiment Name). When you choose a Blank as the sample type, however, the experiment name is not necessary and thus will be grayed out. To collate different measurements (from different data files) for an incremental heating experiment into one and the same age calculation file, always use the same Experiment Name and save the files to the same Project directory (see next step).

In the final dialogbox, you have to set all Sample Parameters necessary to perform an age calculation. The shown fields are always pre-filled with data from the previous calculation, even if these were performed a few days or weeks ago. Completing this dialogbox will be fast, because most entries will be similar and thus don't need changing when regression data from a single (incremental heating) experiment. Most likely, only the GMT datum and Temperature need editing, unless you start to reduce a totally new experiment. If your raw data files already have header lines containing this information, ArArCALC will automatically transfer this header information into this dialogbox by using your Input Filter (see also: Setting the Preferences). Even in this highly-automated setup this dialogbox will be useful to you, because it allows you to check and edit the sample parameters before further processing of the data commences. You can always recall this dialogbox at a later stage in the Raw Data Reduction view of ArArCALC via the Options # Sample Parameters menu in order to edit the sample parameters.

If you have entered all the sample parameters, you will be guided to the Raw Data Reduction view. In this view, a XY-scatter plot displays the measurement time (in seconds) after the inlet of the argon sample in the mass spectrometer on the X-axis, and the intensity of the beam on the Y-axis (in volts, amps or counts). By default, the intensity data for Ar40 is shown first. Each different argon isotope can be calculated by clicking the isotope buttons Ar40, Ar39 ... Ar36. Data points can be included or excluded from the calculations by clicking the toolbar buttons 1, 2, 3, 4 ... 11 that represent the data points, or by clicking the data points themselves on the diagram. Excluded data points are denoted by blue squares and a suppressed toolbar button. The Reset button recalculates including all data points. ArArCALC does not decide which fit to the data (exponentional, parabolic, linear or average) gives the best results. For this purpose, you can set the default regression type for each argon isotope in the preferences (see also: Setting the Preferences). Only in one particular case, when the exponential and parabolic are similar to the linear least-squared fit, ArArCALC accepts a linear fit by default. However, based on the calculation results (see the boxes to the right of the scatter plot) you can always overrule these program decisions yourself, by choosing the appropriate button on the ArArCALC toolbar: Exp, Par, Lin or Ave.

ArArCALC saves all calculated argon intensities of one experiment in one Microsoft Excel 2000-XP-2003 workbook that includes two plateau diagrams and two isochron diagrams, and their respective data tables. The connection between the Raw Data Reduction view (see above) and the Age Calculation view of ArArCALC is easily made through the File # Switch to menu bar item (see also: Switch to ... Option). When you select this option, ArArCALC first saves the calculations and then switches to the age calculation view. You can also make this switch without saving the calculation, by holding down the SHIFT key. If you do not want to switch yet, but you would like to reduce another raw data file, first choose File # Save to save the calculation and then choose File # Open Datafile # Raw Intensity Data to open a new data file.

Note   In order to be able to perform an age calculation, ArArCALC saves the calculated intensities of the latest blank measurement in this workbook (in Editing Data in ArArCALC it is explained how to manually edit the blank intensities later on during the age calculations).

The following data table will be shown in ArArCALC when you switch to the Age Calculation view. In the shown data table, single incremental heating steps can be excluded or included from the age calculation by double-clicking on the Check Mark symbols. This will automatically recalculate the weighted means, isochrons and other statistics. The Reset button recalculates including all data points. In ArArCALC all errors are calculated as 1 Sigma or 2 Sigma errors. You can report the ages in either the Ka, Ma or Ga age units.

Maneuvering between the different data tables (see also: Selecting Different Data Tables in ArArCALC) and diagrams is simply achieved by clicking the worksheet tabs Data Tables, Age Plateau, K-Ca Plateau, Normal Isochron or Inverse Isochron. Below an example is given for a typical age plateau diagram.

Blank and Air Samples

Performing data reductions for Blank and Air Shot measurements starts off the same as for all other measurements. Therefore, the same instructions, as described above, should be followed. ArArCALC saves all reduced blank and air measurements in text files organized per measurement date (blank) or experiment name (air). These files are always stored in the ArArCALC/Blanks and ArArCALC/Airs directories.