Microsoft Excel 2007 Creating a XY Scatter Chart

Transcription

1 Microsoft Excel 2007 Creating a XY Scatter Chart Introduction This document will walk you through the process of creating a XY Scatter Chart using Microsoft Excel 2007 and using the available Excel features to format the Scatter Chart. Sections in this document: Introduction Entering Data Making a Graph Changing the Chart Title Printing and Fine- Tuning Checklist for a Presentable Graph Entering Data The most common way to organize data in Excel is by creating a vertical column with a label in the first row. Example: Solutions of varying concentration are analyzed by an instrument which generates a signal based on the solution concentration. In this case the independent quantity is Concentration and the dependent variable is Signal (we know the concentration, but we have to measure the signal that it causes). This means that Concentration should be on the X-axis and Signal should be on the Y-axis. In Excel, the X-axis values need to be to the left of the Y-axis values.

2 Making a Graph For starters, Excel refers to graphs as "charts". By graphing this data, we can see the relationship between signal and concentration. 1. Select the data to be graphed by clicking and dragging the cursor over the range of cells containing your data (including labels). 2. Select the Insert Tab from the Ribbon. 3. Select the Scatter button in the Charts group and select the first subtype (Scatter with only markers). 4. If the XY Scatter Chart is covering the data, move it by placing your mouse in a blank area of the chart until your mouse turns into a four headed arrow, hold down the left mouse button and drag the chart to a clear area on the worksheet. 2

3 Changing the Chart Title 1. Select the Chart Title above the chart itself and type directly over it with your desired title. If there is no title: 2. Select the Layout contextual tab (these are different colored tabs on the ribbon). 3. Click Chart Title in the Labels group. 4. Select the Above Chart button. The Chart Title text box appears above the chart. 5. Type your chart title and press ENTER on your keyboard. 3

4 Adding Axis Titles Axis labels should include the quantity being measured (data type) and the units (IMPORTANT!). 1. Select the Chart on the worksheet. 2. Select the Layout Contextual Tab from the Ribbon. 3. Click Axis Title in the Labels group. 4. Click Primary Horizontal Axis Title. 5. Click Title Below Axis. 6. Type the axis title you want (Concentration (mol/l) was used in this example) and press ENTER. 7. Click Axis Title in the Labels group. 8. Click Primary Vertical Axis Title. 9. Click Rotated Title. 10. Type the axis title you want (Signal (units) was used in this example) and press ENTER. 4

5 Best Fit Line, Slope and Intercept Often, we need to determine the mathematical relationship between the points on a graph. In the graph above, you can see that the points form a straight line. A best fit line can be added to the graph by the following the steps below: 1. Click once on the chart to select it. 2. Select the Layout Contextual Tab from the Ribbon. 3. Click Trendline in the Analysis group. 4. Click More Trendline Options. The Format Trendline dialog box will appear. 5. Click beside Linear. The equation of that line will follow the form: y = mx + b - where m is the slope and b is the y- intercept. To determine the value of m and b: 6. At the bottom of this dialog box, check the box for Display Equation on chart. You may also want to check the box for Display R-squared value on chart for some graphs. 7. Click Close. 8. When you return to your graph, a new text box will have the equation of the best fit line, along with the R-squared value. Often the text box is in the middle of the graph, so move it to one side by dragging the box. The R-squared statistic measures how well the data fit the model of a straight line. The closer this value is to 1.0, the better the fit of the data to the linear model. In this graph, the points are all very close to the best fit line, so the R-squared value is high. 5

6 Printing and Fine-Tuning When printing, you must make sure the graph is selected. There are several ways to tell this. The graph will have a blue border around it. This shows that it is selected for editing. Also, when a graph is selected, the contextual tabs show up on the ribbon. When the graph is not selected these contextual tabs go away. Changing numbering on an axis 1. Select the Chart on the worksheet. 2. Select the Layout Contextual Tab from the Ribbon. 3. Click Axes in the Axes group. 4. Click Fixed beside Minimum and place a number in the box. 5. Click Fixed beside Maximum and place a number in the box. 6. Click Close. Printing 1. Select the Chart on the worksheet. 2. Click the View tab on the ribbon. 3. Click on the Page Layout button in the Workbook View group. 4. Notice you may add headers and footers by clicking in this area of the spreadsheet and typing the desired content. 5. Click the Page Layout tab on the ribbon. 6. In the Page Setup group, click on the Orientation button to switch between Portrait and Landscape. 7. Click the Office Button and then click Print. The Print dialog box will open. 8. Make your selections and click OK. 6

7 Checklist for a Presentable Graph The following items are required for a good graph (usually, content may vary). 1. Useful title a. More than just "Y vs. X" b. Not just "Concentration", but "Concentration of NaCl in..." 2. X and Y axis labels (with units in parentheses) 3. Appropriate numerical scale on x and y axes c. Conventional increments count by 1, 5, 10, 50 or 100, etc... (or 0.001, 0.005, , etc...) d. Make sure all data are on the graph e. If a point has a y-value of 102 and the y axis only goes to 100, the point will not be visible f. Do not include extra decimals in the axis labels g. If the range is 0 to 200, the numbers should be in the format 0, 100, 200 and not in the format , , etc When printing, choose landscape or portrait depending on what looks best for the graph 7