Reading a thermometer

What it looks like when your child can do it

• — Looking at a thermometer marked every 2 degrees, your child counts the marks between two labels before reading anything.
• — On that same scale, when the line sits four marks below the 10 below label, your child reads 18 below zero, not 2 below.
• — Your child says each reading with its direction, like 20 below zero, instead of only the number.

How to teach it at the kitchen table

1. 01

   Find the zero mark first

   Every reading is measured from zero. Put a finger on it and ask whether the red line stopped above it or below it. That settles the direction before any counting starts.

2. 02

   Work out what one small mark is worth

   Find two labeled numbers, like 0 and 10, and count the spaces between them. Five spaces means each mark is worth 2 degrees. A child who assumes every mark is 1 degree will be off on scales like this.

3. 03

   Below zero, count away from zero

   Under zero the labels read 10, 20, 30 going down, and they mean 10 below, 20 below, 30 below. If the line is 2 marks under the 30 below label on a 2 degree scale, that is 34 below zero, not 26.

4. 04

   Check which scale you are reading

   Many thermometers show Fahrenheit on one side and Celsius on the other. Water freezes at 32 on the Fahrenheit side and at 0 on the Celsius side. Minus 40 is the one reading where the two scales agree.

5. 05

   Make reading it a morning job

   Hang an outdoor thermometer where your child can see it and ask for the reading every morning for a week. Each reading gets said as a number with a direction, like 18 below or 5 above.

You will need: An outdoor thermometer · Paper and a pencil to draw a scale

Try it together

1. Try 1

   On a thermometer marked every 2 degrees, the line stops 3 marks above the 20 label. What is the temperature?

   Listen for  26 degrees. Three marks of 2 degrees is 6 degrees above 20. If your child says 23, they counted each mark as 1 degree.

2. Try 2

   On the same thermometer, the line stops 4 marks below zero.

   Listen for  8 below zero, or minus 8. Watch that your child says below, or writes the minus sign, and not a plain 8.

3. Try 3

   On the same thermometer, the line stops 3 marks below the 30 below label.

   Listen for  36 below zero, or minus 36. A reading of 24 below means your child counted back toward zero instead of away from it.

4. Try 4

   The line stops right on the 40 below label. What is the reading, and what does the Celsius side show?

   Listen for  40 below zero, or minus 40, and the Celsius side reads minus 40 too. It is the one temperature where both scales agree, and a hard cold snap in Glennallen can reach it.

5. Try 5

   The morning reading is 12 below zero. By afternoon it is 6 above. How many degrees did it warm up?

   Listen for  18 degrees: 12 degrees up to zero, then 6 more. If your child says 6, they subtracted 6 from 12 without crossing zero. This is the stretch question.

Watch for

• — Counting the wrong way below zero, toward the zero mark instead of away from it. Saying the word below out loud with every reading keeps the direction straight.
• — Assuming every small mark is 1 degree. Count the spaces between two labels first.

If it is not there yet

• — Go back to readings above zero on a scale where each mark is 1 degree, until counting on from a label is steady.
• — Draw a tall thermometer on paper with zero in the middle, like a number line standing up. Mark readings on it together, above and below zero, and say each one aloud.

A few days of this is normal, and it is time well spent. The lesson will still be there, and it will go faster.

Where this skill comes up

• Grade 6 Math Practice Workbook · Lesson 10

  Below Zero: Positive and Negative Numbers

  Needs it because the anchor example is temperature and the child must read one.