Creating Computational Models with Excel
(AKA Excelettes)
Purpose
Learn how to use Excel to create computational modeling tools that incorporate easy-to-change variables
so as to quickly illustrate their impact on a system’s behavior or output.
Creating an Excel Computational Model
1.
Select an activity or experiment to model.
2. Analyze the experimental scenario and
process:
a. What is the question that your
experiment will answer?
b. What is the outcome or result that you
are watching?
c. What factors (variables) affect the
results?
d. Which of these factors will you keep
constant throughout the experiment?
e. Which of these factors will you
intentionally vary to see how they affect
the results?
f. Which factors will you ignore?
3. Write the equation that relates the
variables to the results.
4. Open Excel and display the Developer Tab
(Win) or the Forms Toolbar (Mac).

a. Windows Office 2010: File -> Options > Customize Ribbon. Choose
commands from: Main Tab. Click to
highlight Developer (do not expand).
Click Add. Click OK.
b. Windows Office 2007: Microsoft Office
-> Excel Options -> Popular -> Show
Developer Tab in Ribbon.
The Home Faucet Audit Example
1. The Home Faucet Audit
2. The Home Faucet Audit Scenario
a. How much water do we use each day via
the bathroom faucet?
b. Amount of water used (daily-usage)
c. Factors that affect how much we use:
i. How often we turn on the faucet
(frequency)
ii. How long the faucet is on with each
use (duration)
iii. Why we turn on the faucet (purpose)
iv. How much water flows from the
faucet each minute (flow-rate)
d. Constants: flow rate
e. Independent variables: frequency,
duration
f. Ignore: purpose
3.
gal 

 min  # times
gal 
Flowrate
xDuration secx
x
 Usage 

60sec   day 
min 
day 
c. Mac: Views -> Toolbars -> Forms.
5. Format a spreadsheet:
a. Enter a title into Row 1 that is
descriptive of the experiment.
5. Home Faucet Audit spreadsheet set up w/ the
experiment’s question as the title and
descriptions of the variables used as column
headings.
Tip: once all of your column headings are in
place select all of the Row 1 cells across the
columns in use and click the
icon to merge the Row 1
cells and center your title.
b. Enter column headings into Row 2,
assigning one column to each
factor/variable identified and one to
the result.
Tip: if your column headings are long, click
on the
icon before starting to
type. This will force your heading to stay
within the width of the column. You won’t
need to use multiple rows of cells for your
multi-line headings.
Tip: adjust column widths, font sizes and
types, colors etc. to make your spreadsheet
easy to read.
6. Set up data entry:
a. Enter the equation from above into
Row 3 of the results column.
Tip: Use the Insert Function feature,
to “build” your equation.
6. Home Water Audit example data entry set-up:
a. Entering the equation:
,
b. Leave the row under the column
heading blank. Draw a value slider into
the second cell under each factor’s/
variable’s heading.
Tip: for the Home Faucet Audit example,
under the purpose column, merge cells A3
and A4 so that one purpose brackets two
rows, one for the value and one for the slider
bar.
Windows Office 2010:
 Click on the Developer Tab
b. Adding a scroll bar for the number of times a
water use/purpose happens each day:


Click Controls -> Insert
Click Form Controls -> Scroll Bar
Mac:
 On the Forms toolbar,
select the Scroll Bar:
Form Control. It is the
5th one down on the
left hand side.
i. Having selected scrollbar tool, click and drag
to draw your scroll bar
near the target cell.
Tip: whenever the anchors (corner
boxes) are showing on the scroll bar,
you can move it around to position it on
your screen. Use the arrow keys on the
keyboard for fine-control over the scroll
bar position.
ii. Right click on the scroll bar and
select “Format Control”.
iii. In the Format Control dialog box,
set the Current Value = the default
value of this variable; Minimum
Value = lowest value this variable
could have; Maximum Value =
highest value this variable could
have; and the Incremental Change
= smallest change possible (usually
the significance of this value).
Tip: All values must be whole numbers.
Tip: You do not need to change the
Page Change control value.
iv. Click on the icon next to the Cell
Link field,
. A Format control
window will open.
v. Click on the cell above the scroll
bar / below the column heading.
The cell address will appear in the
Cell Link field.
vi. Hit the Enter key and click OK. The
numerical value of this variable
will display in that cell.
c. Your model is complete; try it out!
c. The completed model: sliders have been
adjusted to enter realistic values. The values
can be easily increased or decreased to see
what impact changes in “brushing teeth”
would have on water usage.
Summary/Analysis of the Home Faucet Audit Example
In the example, we created an Excel file to model water savings. Here is how it works.
1. If my faucet flow rate is 3.5 gallons per minute, and I have the water running for 240 seconds (4
minutes), while I brush my teeth, I will use 14 gallons of water each time I brush my teeth.
2. Since I brush my teeth 2 times/day, this amounts to 28 gallons/day.
3. If all 4 people in my family do the same thing, we are using 112 gals/day for this purpose.
4. I can think of having everyone in my family reduce the amount of time they have the water running to
60 seconds by turning the water off and on during the brushing. I can test my idea by adjusting the
slider(s) on the computational model and quickly see that it will result in our family using only 28
gals/day for teeth brushing!
This tool is a quick, easy, informative, and motivating way to evaluate the impact of input variables on the
output of an experiment!