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Guide to I Chi Spreadsheets This folder contains electronic models for examples presented in this book. The models are constructed in Excel workbooks with spreadsheet calculations to illustrate isotope examples of Chapter 7. To orient yourself to what is supposed to happen in these workbooks, you may want to find the corresponding section in the book, then read the text about that example before actually opening a workbook. When you open the workbook, you will find spreadsheets that generally have master variables in the upper left sections. These master variables are highlighted in bold and are there for you to manipulate. Type in a value and watch what happens in the isotope graphs. Change those master values to get a feeling for linkages between mixing and fractionation, the big themes of the book. One of the simplest and most informative things to do in each spreadsheet is to set fractionations equal to zero, so that only mixing controls dynamics. Change the gain terms, then the loss terms and observe the effects on mixing. After understanding these mixing effects, then turn on fractionation again by typing in a non-zero fractionation value, and watch what happens. Try it! With gains and losses involved in mixing fixed at constant values, you can evaluate fractionation. And don’t forget to try various combinations of the individual mixing and fractionation values you have been using – the combined effects are most complex, and most interesting. In sum, try manipulating the master variables in the spreadsheets of this Appendix – you may be surprised how much isotopes change, depending on how you set up mixing and fractionation in these examples. In some examples, you may find that changing master variables leads to odd and nonsense results. Two particular problems deserve mention. First, when loss terms are too great, pools or reservoirs start to have negative values and many odd features result in the I Chi graphs. If this is happening, make the loss terms smaller, so that amounts in pools always stay positive. Second, changing master variables can give data off the charts, beyond the normal scales. To reset the scale of an x-axis or y-axis in a graph, use your cursor to click on the axis. A box labeled “format axis” should appear. Click again on the tab labeled “scale”, and reset the “maximum” value to a higher number, then click on the “ok” button. The scale will reset, and now your data should appear on the chart. Back-up versions of the workbooks are provided, so that if you change variables and overwrite the original material, you have a spare copy to use for reference. Generally, if you want to save your work, you can make your own copy of the workbook and save your work therein. Beyond simply typing in different values and saving your new scenarios, also you can access the mathematics in these worksheets. You can look more closely at the math underlying the spreadsheets by clicking on individual cells, examining the formulas used at each location. Those formulas appear in the toolbar line just above the worksheet, and if you use your cursor to click on the formula there, color highlighting appears so that you can see spreadsheet values used in the equation. The examples have similar math, the “I Chi” equations introduced in section 4.3. Calculations are done sequentially in horizontal rows in the spreadsheet, with the results in the final columns copied into the first columns of the next row. Each row represents one time step with typically several processes happening across the columns in that time step/row. This is the step-by-step philosophy of I Chi. There are detailed examples in Section 4.4 about how this math is set up and actualized in the spreadsheets – consult that section 4.4 to get a feel for how the calculations are set up in a sequential manner in rows and columns. Finally, you can write your own examples, and introduce your own I Chi equations, amending the workbook models. The equations are actually simple algebra, summarized in Section 4.3. Writing your own I Chi is not nearly as hard as it may look at first glance, but then again, thinking with math is its own challenge. Special notes on individual workbooks of this Appendix 1: Workbook 7.2, Isotopium. The fractionation factors of this workbook 7.2 follow a slightly different usage than in the rest of this book. Fractionations are given in terms of heavy/light isotopes instead of light/heavy isotopes for the closed system reactions of this workbook. Thus, the workbook uses - instead of and H/L instead of L/H. These differences are explained in Box 2.1 in Chapter 2. The reason for this switch is to follow closely the derivations for closed system equations given in Section 7.3. In most cases, you can substitute – simply for values where the fractionation is 100o/oo or less because - and will have the approximately the same value (see Box 2.1). For larger fractionations, however, there is a difference, especially that - values cannot exceed 1000o/oo, while values can.