lesson
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If you leave a cup of water outside on a freezing winter night in Alaska, the temperature might drop far past the freezing mark.
To measure how cold the air gets past zero, thermometers use negative numbers, which are values less than zero written with a minus sign (−).
A standard vertical thermometer is just an upright number line with zero acting as the divider between warm and freezing.
📊Create an interactive or animated vertical thermometer graphic side-by-side with a vertical number line. The thermometer tube has red liquid. The center line is 0°C. Above 0°C, the scale is colored warm orange/red with labels +5, +10, +15, +20. Below 0°C, the scale is colored cool icy blue with labels -5, -10, -15, -20. An indicator arrow points to the level of the liquid at -8°C with a label: '8 degrees below zero = -8°C'. Clean modern card UI, white background, readable font, 350px width.
How do you read the exact mark when the liquid level falls between numbered lines?
Reading Vertical Thermometer Scales
Before reading any thermometer, first find the scale interval, which is the value each tick mark represents.
Count the number of spaces between two labeled numbers, then divide the total difference by that number of spaces.
📊Visual diagram showing two zoomed-in thermometer scales to demonstrate finding the scale interval. Scale A: Labels at 0 and 10 with 5 equal spaces between them (each tick = 2°C). Scale B: Labels at 0 and -10 with 10 equal spaces between them (each tick = 1°C). Step-by-step annotation: 'Difference ÷ Spaces = Value per tick'. High contrast, clear tick marks, warm/cool gradient styling.
Let's read a thermometer where the major marks are every 10∘C and there are 5 equal spaces between them.
Since 10÷5=2, each tick mark represents 2∘C. If the liquid is 3 ticks below 0∘C, count downward: −2, −4, −6∘C.
A common mistake is counting upward from a negative label like −10. Always count downward from zero when reading negative values, or count upward from the lower negative number (from −10 up two ticks of 2 gives −6).
What happens when you look at a digital screen instead of a liquid tube?