This lab document covers measuring variability due to instruments and making box plots. It instructs students to bring their lab manual, print materials before class, and submit individual work. The point is that imprecise instruments like a yardstick marked every 6 inches can affect measurements, and randomizing orders reduces bias. Students should learn how instrument variability impacts results and how to calculate statistics like median, quartiles, standard deviation to make box plots from a data set.

1. Lab #3
Variability due to the measuring instrument

2. What to keep in mind
• From next week if you don’t bring your lab manual, you’ll be
penalized.
• Online book -> Print before lab starts, so you can write on your paper
• Need to submit individual work. (even when you worked in a group)
• If you have a valid/documented reason for missing lab, please send a
mail to your lecturer (not lab instructor) before lab.
• Lowest lab grade will be dropped
• Keep your graded work – in case I make a mistake in the gradebook

3. The point of this lab
• Imagine trying to measure a bug using a yardstick that only has marks
every 6 inches
• Imagine trying to measure a small amount of milk using a measuring
cup that only has lines every cup
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2
3

4. What you should learn
• The effect the measuring instrument has on the variability of your
measurement
• How to find median, Q1, Q3, min, max and then make a boxplot from
them
• Why to randomize the order when you’re taking different measurements
• How to calculate standard deviation

5. Write this in your lab book!
Why do a random order
like this?

6. 10 8 14 2.5 13 10 3.5 2.1 1 5.5 3.8 12
Step 1: Put the data in order (smallest to largest)
1 2.1 2.5 3.5 3.8 5.5 8 10 10 12 13 14
Step 2: Find middle of data (the median)
1 2.1 2.5 3.5 3.8 5.5 8 10 10 12 13 14
6.75
Step 3: Find Q1 and Q3
1 2.1 2.5 3.5 3.8 5.5 8 10 10 12 13 14
6.75 11
3
Step 4: Find Min and Max
1 2.1 2.5 3.5 3.8 5.5 8 10 10 12 13 14
6.75 11
3

7. Min Q1 Median Q3 Max
1 3 6.75 11 14
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12
15
14
…and you draw your
second box plot here
beside the first