Microsoft Excel Tutorial for Calculations and Graphing

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1 Microsoft Excel Tutorial for Calculations and Graphing Introduction How many times have you done multiple repetitive calculations, punching long strings of calculations into your calculator only to find that you made a simple error, requiring you to reenter the calculation, or had to do the same calculation multiple times for a large set of data? The spreadsheet program Excel produced by Microsoft can quickly complete these calculations for you, and gives you the ability to proofread your work. For this reason, it is very useful in education, and the public and private sector workforce rely heavily upon its use. For these reasons, it is important that you become proficient in its usage. This guide was written for use with Microsoft Excel 2010 on a windows computer, but other versions are similar. The Macintosh version of Excel is visually different, but the same types of ideas can be used to complete the exercises contained here. Spreadsheet Basics Once in the Excel program, you will see a white workbook with individual boxes (cells) which are designated by column and row. For example, the top left cell in the spreadsheet is A1. The cell one space down is A2 and the one to the right of A1 is B1. You can highlight specific cells by clicking INSIDE the cell and dragging the mouse, entire rows or columns can be selected by clicking on their heading. You can enter numbers, text, or formulas into individual cells by typing in that cell. Pressing ENTER moves you down a column. Pressing TAB moves you across a row. The arrow keys can also move your cursor between cells. A new workbook contains three separate worksheets, accessed by clicking the tabs at bottom of the worksheets, labeled Sheet 1. You can insert a new sheet by clicking INSERT, then WORKSHEET. You can delete sheets as needed, and can rename the sheets by right clicking on the sheet name. These sheets can be utilized to categorize sections of information as needed. Exercise 1: Begin by entering a made up set of data onto Sheet 1, as shown in Figure 1. You can utilize the format buttons above the workbook to format the text as you see fit. If your columns don t expand so you can see all the text in each cell, you can hold your mouse cursor over the division between columns until your cursor turns into a vertical line with an arrow on both sides and double click your mouse to auto fit the column width. In order to ensure the correct numbers of significant figures are displayed, highlight the cells, right click, and use the format cells option, category: number options to set the number of decimal points that should be displayed. This dialog box is shown in Figure 2. If you must enter the same number multiple times (like in Column D) use the fill command. Highlight the cell in D1 and drag down to D7. Now look to the menu buttons across the top of the screen for a fill button way over in the Editing section. If you click this button and select down, it will fill the into each cell. Notice that units are displayed in column titles not after each individual measurement. There should be nothing except numbers in the individual cells containing number so calculations can be carried out later.

2 Figure 1: Exercise 1 Spreadsheet Setup. Figure 2: Format Cell Dialog Box Calculations By now you have an understanding of data entry into the Excel spreadsheet, but the program can do so much more than just categorize data into neat tables. We can easily utilize it to do repetitive calculations on the different portions of the data. Excel recognizes that the user wants some type of calculation in a cell if the user uses an equal sign to start the cell. This is called a formula. Excel will follow the mathematical order of operations inside a cell, so the user must make use of parenthesis as needed. In addition, Excel has a multitude of built-in

3 calculations sets called functions that can represent easy calculations such as average up to advanced calculations that are beyond the scope of this primer. In Exercise 2 you will use simple arithmetic to calculate values for cells, both simple and complex, and then utilize two common functions that calculate the average and standard deviation for a data set. Exercise 2. Using the spreadsheet prepared in Exercise 1, the mass of water can be calculated (Column E) as the difference between columns C and B. Type into cell E3 =C2-B2 and hit return. Notice how excel calculates and then displays the result of this calculation automatically. Alternatively you can type the equal sign and then click on the cell C2, press the minus key, and then click on cell B2 to get the same result. Since these calculations are very repetitive, you can use the fill down command again to copy the formula from E1 down to E6. Notice how Excel increments C2 to C3 for the next cell down. If for some reason you don t want this to happen you can use absolute cell references, by putting in C$2 instead of C2 in the formula and Excel won t increment the cell number each time. In this case, the automatic increment suits our needs (you would only use the absolute references for constants and other static values). Calculate the density of water using two different methods. Into Cell F2, type =E2/D2 and then in Cell G2 type =(C2-B2)/D2. After you fill both columns down, notice how the same number results. In this way, Column E is really not needed. If the data analysis needs complex calculations, you can utilize Excel s built in functions such as Average and Standard Deviation. Calculate the average of the experimental densities in Column F. In Cell F9, begin typing =Average(. A tool tip appears to help you select and use various formulas. At this point you can select the cells of which you want to find the average. You can either type the range in the format F2:F7, or use the mouse highlight the cells. Then insert a close parenthesis and hit return. Your formula should be =Average(F2:F7). You also want to find the standard deviation of the set of data, this function starts out =STD but which selection should you choose? In science, one can rarely measure all of something, so a good selection would be =STEDEV.S(F2:F7) because we are measuring a sample of real values. Of course, the cells contained in Figure 3 should be formatted to follow significant figure rules, we have not done so to show you the results of the calculations, but you should always remember to report results to the proper number of significant figures. Excel contains a multitude of built in functions for higher level statistics and business modeling, but they are beyond the scope of this exercise. Figure 3 shows you a selection of the results of the calculations thus far (columns B-D have been hidden for clarity).

4 Figure 3: Exercise 2 Calculations and Formulas Graphing The Excel program is also good at creating graphs and linear regression best fit lines. In the following example, you will use a sample data set to create a graph with two sets of data, then do a linear regression calculations to determine the slope, intercept, and r 2 values. You can also determine these values in the spreadsheet itself using the built in functions Slope, Intercept, and RSQ respectively. Exercise 3. For this exercise, you need to create a new data set. Into a new sheet in the same workbook, enter the information contained in Cells A1 to C8 of Figure 4. For now, ignore the information in Rows You are going to calculate those values after you create your graphs to compare. Figure 4. Exercise 3 Spreadsheet values and calculation results. Once the data is entered, create a simple graph. Put your cursor into an empty cell, go to the insert menu, then the charts section. Click the scatter button and select the graph that does not connect the points.(see Figure 5).

5 Figure 5. Exercise 3 Insert Scatter Plot Menu Options. You should now see a blank white area in the spreadsheet, right click in that box and go to select data. In the select data source window that opens click the add button under the legend entries box. An edit series window pops up (see Figure 6). Put your cursor in the Series Name box and select Cell B1, this will label our data set. With your cursor in the Series X Values box, click in the worksheet and highlight cells A2 to A8. In the Series Y Values box, again place your cursor, but also delete the ={1} that is in the box and then highlight cells B2 to B8. Once these steps are complete, your box should look like Figure 6. After clicking the OK button, your graph will auto update so you can start to see what your data looks like. Try reproducing the above procedure to add a second series to the same graph using the Absorbance (400 nm) data. Figure 6: Edit Series Dialog Box. At this point your graph is starting to take shape, you need to label the x- and y-axis, and customize the graph. Under the new chart tools menu select the layout tab as shown in Figure 7. You can now click on the axis titles button and add primary x- and y- axis titles. This will add titles to your graph that you can now click on and edit as needed. Make sure to add units to your graphs so readers know what type of scale you have. Next you can go to the gridlines button and remove or add gridlines as needed. For this graph (Figure 8) the gridlines were removed to create a cleaner look.

6 Figure 7. Exercise 3 Chart Layout Menu Bar. Figure 8. Exercise 3 Graphed results You should then edit the x- and y-axis ranges to make your data fill up most of the available space. To do this, click on the axis to select it, and then right click to get to the Format Axis window (Figure 9). Change the axis options to set the minimum and maximum values slightly larger than your data set. Do this as needed to each axis individually.

7 Figure 9. Format Axis Window The last step for the graph is to add a trend line to each data set. Single click on a point in the data set, right click and select add trendline. In this case you are using a linear regression; click the check boxes to display equation and R-squared values on the cart and click close. Do this again for the second data set, and you should end up with a graph that is similar to Figure 7. Figure 10. Add Trendline Window

8 To print just the graph sized to fit a page, select the graph by clicking it, then go to file and the print option. You can also calculate the slope, intercept and R 2 values directly in the worksheet, but this method shouldn t take the place of constructing a graph (which gives you a much better idea of the quality of your data). To calculate the slope, use the slope function. In The cell B10, type =SLOPE(. At this point the tooltip is telling you to input the known y-values, so highlight cells B2:B8 by clicking in B2 and dragging to highlight cell B2. Type a comma and the tooltip asks you to enter the known x-values, so this time use cells A2 to A8 and then type the close parenthesis and hit return. Your formula should look like =SLOPE(B2:B8,A2:A8). If we copy this cell and put it into cell C10, Excel increments the row heading to =SLOPE(C2:C8,B2:B8) and this is an error (the y axis is correct, but the x-axis is not). We can go into Cell C10 and repair the formula directly to use the correct cells, or we can go back to Cell B10 and utilize at $ to stop Excel from incrementing the column letters when copying. So change the formula in Cell B10 to =SLOPE(B2:B8,$A2:$A8) and then copy it to cell C10. Notice how Excel did not change the known x-values, but did change the known y-values. Now try to calculate the intercept and R 2 values on your own using the Intercept and RSQ functions respectively. Check your values with those shown in Figure 3. Conclusions This has been just a brief introduction to Microsoft Excel. This program has many additional features and the ability to do complex calculations, many of which are explained in the program s help menu. In addition, there are many great tutorials online that can give you more information.