Math · Ratios & measurement
Time, Temperature, and Applied Measurement
Estimated time includes reading and one quiz. Take the time you need.
Start here: key ideas
- Elapsed time is an interval, not a clock reading.
- 24-hour times after 12:59 subtract 12 hours for p.m. time.
- Celsius and Fahrenheit conversions require both scaling and an offset.
- A measuring tool supports only the precision shown by its divisions.
What you’ll be able to do
- Find elapsed time across an hour or midnight.
- Convert between 12-hour and 24-hour time and between Celsius and Fahrenheit.
- Read a measurement scale to its supported precision.
Elapsed time is an interval, not a clock reading. 24-hour times after 12:59 subtract 12 hours for p.m. time.
Optional review
If you’d like to review the basics, visit Measurement Systems and Unit Conversions. You can start this lesson without completing those first.
Find elapsed and military time
Elapsed time is the distance from start to finish. Worked example 1: From 9:47 a.m. to 12:18 p.m., move 13 minutes to 10:00, 2 hours to noon, and 18 minutes to 12:18. Total: 2 hours 31 minutes. This avoids subtracting minutes that would require borrowing.
In 24-hour time, 0000 is midnight and 1200 is noon. For a p.m. time after noon, add 12 to the hour: 7:25 p.m. becomes 1925. For 2040, subtract 12 from 20 to get 8:40 p.m.
Convert temperature with order intact
Use F=(9/5)C+32 and C=(5/9)(F−32). The 32-degree offset means temperature conversion is not a simple ratio. Worked example 2: Convert 68 °F: C=(5/9)(68−32)=(5/9)(36)=20 °C. Subtract before multiplying.
Read only justified precision
First find a scale interval: subtract labeled values, then divide by the number of equal gaps. If 10 mL and 20 mL labels have five equal gaps, each gap is 2 mL. Read the bottom of a liquid meniscus when the tool calls for it. Report the value only as precisely as the markings support; extra decimal places imply information the instrument did not provide.
Clock arithmetic is base 60. A decimal duration of 1.30 hours is 1 hour 18 minutes because 0.30×60=18; it is not 1 hour 30 minutes.
Across midnight, split the interval. From 10:50 p.m. to 1:20 a.m. is 1 hour 10 minutes to midnight plus 1 hour 20 minutes, totaling 2 hours 30 minutes.
Check temperature against anchors: 0 °C=32 °F and 100 °C=212 °F. An extreme result for room temperature signals an order or offset error.
On an analog scale, count equal spaces between labels. Report only the precision supported by the smallest division and any permitted estimate between marks.
For schedules, decide whether both times share a.m. or p.m. and whether the end occurs the same day. Writing the date beside times prevents an accidental negative interval.
Temperature change is different from temperature reading. A rise of 9 Fahrenheit degrees equals a rise of 5 Celsius degrees because interval sizes scale by 5/9; the 32-degree offset applies to readings, not changes.
When reading liquid volume, keep the eye level with the surface to avoid parallax. Identify whether the scale increases upward or downward and use the requested part of the meniscus.
A reported measurement combines a number and unit. Writing 7.5 without mL, cm, °C, or minutes leaves the result uninterpretable and can hide use of the wrong scale.
Terms to remember
- elapsed time
- The duration between a start and an end.
- 24-hour time
- A clock system numbered 0000 through 2359.
- degree Celsius
- A temperature unit with water freezing near 0 °C.
- degree Fahrenheit
- A temperature unit with water freezing near 32 °F.
- scale interval
- The value represented by the gap between adjacent marks.
- precision
- How finely a measurement is reported.
Your quick summary
- Elapsed time is an interval, not a clock reading.
- 24-hour times after 12:59 subtract 12 hours for p.m. time.
- Celsius and Fahrenheit conversions require both scaling and an offset.
- Read each instrument to its marked precision and report the measurement with the correct unit.
Lesson quiz
Check what you learned, then review the explanations. This quiz saves results on this device only. Sign in to save quiz results to your account.