Intro to SigmaPlot

For those with experience in Microsoft Excel, SigmaPlot will be a fairly intuitive program to use.  Still, the program does present some challenges as you try to customize graphs and can take a little getting used to.

When opening SigmaPlot, you are first presented with a spreadsheet.  To begin graphing, one should copy and paste relevant data into the spreadsheet.  Generally, it is best to have each series of data in a given column.

Once the data have been inserted, you can choose among the different graph types using the icons on the left hand side of the SigmaPlot window.  It is generally worth exploring the available options, as each plot has its own unique characteristics. For example, one plot may allow for a single series of data while another might allow for multiple series.

Once you have selected a plot, follow the prompts to select your data. For the above example we have chosen a "Simple Line & Scatter-[with] Error Bars". We will use this to plot the average body weight of rats across days of an experiment. Having selected our graph, we designate in the first menu that our data are arranged in columns and then (for this example) can select either that we have "XY pairs" or a "Single Y" in the subsequent menu.  Given that our X-axis consists of incrementing integers (number of days), we can select Single Y and allow SigmaPlot to fill in the integers for each day (1-21) or we can select XY pairs and use a column we have filled with numbers 1-21 (col 1, above).  Finally, as described in the sigma plot menu, we will use the mouse to select columns corresponding to our X series (if XY pairs), Y series, and Error terms. Click "finish". Congratulations! You have made your first graph.

To make most changes to the graph, one can right click on the graph and choose "graph properties". This allows you to change an array of properties including the symbol types, error bar style, line style, or scaling of the X and Y axes. Most of these values can be adjusted using the user interface by adjusting the provided slider bars or changing the values in an input box.

For those that are new to SigmaPlot, exploring these menus is one of the most beneficial things you can do.  For practice , you might take a very simple graph and plot is with a number of different settings.  As a careful scientists, you would do best to change one thing at a time so that you can see your changes take effect.

It should also be stated that properties of the plot can sometimes changed by using your mouse to select a specific part of the graph. This can be done to edit text for things like the axis labels by simply clicking on these items and typing in the new lab. Similarly, you can edit other properties of items (e.g. the color of text or lines) by right clicking that particular item, and selecting the properties for that specific item (e.g.,"text properties" for the Y axis labels). Selecting individual items in this way can also be used to delete specific components of the graph, move certain items, etc.

One final problem we will explore is how to use text for the tick labels on an axis. To do this, you first need a column filled with strings (text) that represent your data.  For the current example, we will use 21 letters of the alphabet in place of day numbers.  Once we have a column with letters A-U (C), we enter the graph properties (See above), select the axes tab, and click the "Tick Label" icon in the left-hand menu (A). Under the top pull down menu (type), select the column number containing your axis labels. Next, you may need to enter the left-hand menu for "Ticks" (A) to change the tick interval to "Manual" (B) and select the number corresponding to the desired tick interval (every X data points starting at Y).

NOTE: One quirk of SigmaPlot is that it often applies labels that include strings such that they do not line up with your data points.  This can easily be fixed by inserting a blank cell before or after the cells containing your labels in order to line the correct label up with the correct data (Notice the blank cell at C, above which changes the labels from #'s 0-20 to #'s 1-21).

Now that you have an introduction to SigmaPlot, you can begin learning how to perform more advanced tasks.  You can find some other SigmaPlot tricks here, or you can start playing around with the things you learned today.  Happy Graphing!

    David Barker

My final graph after doing a little playing: