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8/7/2019 Activity Excel

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How to plot a data set

You need to know how to use Excel to plot data that you have entered (or calculated) in a

worksheet. This appears to be a daunting task at first, but if you follow the steps below afew times it will become automatic. Let's plot the data table above.

1. Enter your data onto a worksheet as shown in the above screen shot. If you payattention to the title and column headings now, it will prevent confusion when youcome back to the worksheet later.

2. Select all you have entered including the titles. Then click in the main menu onINSERT. A Chart Ribbon will open. Choose the XY (Scatter) button.

(DISPERSION)

3. Then select the sub-type that does not connect data points with lines or smoothcurves.


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4. The graph will appear on the same page as the data (as shown below).

If you decide to print the graph as a new sheet, simply right-click (ctrl-click on a Mac) on

the Chart Area, select MOVE CHART, and a window will open allowing you to set thechart in the current page, or into a new page.

Adding a trend line to the plot

To add the trend line, click on one of the data points on the graph to select them, then right

click (CTL-click on Mac) to open a contextual menu, then select Add Trend line from themenu. It should be under Tools of the graph.


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Click Analysis. And then choose trend line.

It is possible with Excel to add trend lines otherthan linear ones. For example, you may

choose logarithmic, exponential, polynomial, power series, or a moving average, dependingon the trend(s) displayed by the data.


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To display the equation and R-squared value on the graph, clickAnalysis, on the Options

tab (mas opciones de la linea tendencia). Then place check marks in the appropriateboxes. When the OK button is pressed the best fit line is drawn and the equation of the line

andR

-squared value will be displayed on the graph. You may move the equation byclicking and dragging it to the desired location.

The R-squared value is actually the square of the correlation coefficient. The correlationcoefficient, R, gives us a measure of the reliability of the linear relationship between thex

andy values. A value ofR= 1 indicates an exact linear relationship betweenx andy.Values ofRclose to 1 indicate excellent linear reliability. If the correlation coefficient is

relatively far away from 1, the predictions based on the linear relationship,y = mx + b, willbe less reliable.


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To display the axes labels, open the hermanitas de graficosclickPresentacion, and

then clickritulos del eje

and then enter the horizontal axis title and same for y-axis.


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Altering the look of a displayed equation

You might find it odd that the equation displayed on the graph is y = 1.07x+ 0.024 Afterall, we did not measure y's and x's, but rather we measured protein concentration andabsorbance. You should always change the displayed equation to match your measured

variables!

y To change the equation, simply click on the equation and change the variables.y By doing this step, you are in essence telling your instructor that you really do

understand what was actually measured and how well the experimental datamatched the theory.

The final result of your efforts is a graph that looks something like the following:


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This is certainly adequate for your personal notes but it would not receive much

credit if it were submitted as part of a lab report. Read the section of the style

manual on graphs and adjust the appearance of your graphs to comply with it.

1. Remove the grid lines. Click on any grid line and press the delete key

2. Remove the graph pane shading. Right click (control click on the Mac) on the graphpane and select format plot area and finally select no fill.

3. I always delete the default legend box. With just one set of data on the graph, thelegend is not useful. Even with more than one series, the information in the legendbox is more appropriately in the text of the legend below the graph and you can

simply copy its contents and paste them into the legend text box below the graphpane. To delete it, simply click on it and press the key

4. Remove the title and replace it with a written legend including the figure number,title, and description of the graph. The default

E

xcel graph is not intended forpresentation in a scientific report, but rather as a presentation graphic for projection.The easiest way to add a proper scientific legend to a stand alone Excel graph is to

insert a text box. This can be done from the drawing toolbar. Click on the text boxicon as indicated below and draw a box under the graph pane. Type your legend in

the box and adjust the size and position to suit your text. It may be necessary to

click on the graph pane and readjust its height to accommodate the box.


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Note that it is also possible to change the font style and size of the titles and

headings.Exel assumes that your graphs will be used for projected presentation andthe default fonts are to large to look appropriate in a written report. If your graph is

to be incorporated into a lab report it would be appropriate to change these to matchthe rest of the report. Simply right (control) click on a title or axis and select font.

You can now change the font

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