Measure angles to the nearest degree
Position a protractor, choose its correct scale and measure acute, obtuse, tilted and reflex angles to the nearest degree on explicitly accurate diagrams.
Section 4.4 · Measures
Exam scope and assessment notes
Foundation and Higher share the seven published F:4.4A–G Measures rows. The Higher table says See Foundation Tier; there are no additional H4.4 rows. The chosen eight-lesson split covers instrument scales, time intervals, estimates, nearest-degree angle measurement, three-figure bearings, average speed, density and pressure. Eight lessons and thirty-two original worked/staged cases are StudyForA’s design, not a syllabus-prescribed count. Each structural source link requires the corresponding complete teaching record carrying that source ID, a worked explanation and all Guided, Independent and Transfer stages. F4.4F requires the complete speed lesson; broad F4.4G requires all three speed, density and pressure lessons, not a speed-only partial link. Source binding and substantive structure must belong to the same record; a separate untagged duplicate cannot supply missing evidence. These are structural links, not exhaustive subskill or specialist approval. Preserve the actual calibrated instrument ticks, pointer/meniscus positions, ruler endpoints, units and protractor alignment action. Read labelled scales rather than assuming CSS pixels are millimetres. Use only diagrams explicitly supplied as accurate for measurement; ordinary examination diagrams need not be to scale and must not be measured without instructions. Numerical reference readings, protractor openings and the measured bearing remain hidden before a calibrated learner attempt; revealing a reference is not proof of instrument operation. Keep ideal model values separate from approximate human readings and nearest-degree rounding; no universal automatic tolerance or measurement competence is established. Bearings start at the named origin and run clockwise from declared north, with parallel north assumptions stated and leading zeros retained. Distinguish reverse rays, interior route angles and forward heading changes; no magnetic or globe-navigation correction is inferred. Clock intervals retain am/pm, noon/midnight and day order. Average speed uses total route distance over the full named elapsed interval, including stated stops; displacement and instantaneous speed are different. Calculating time by division requires positive speed: at constant zero speed a positive distance is impossible, while zero distance alone does not determine elapsed time. Keep density mass/volume units compatible and volume positive; liquid displacement is final minus initial level. Combined volumes are added only under the stated no-void/no-volume-change assumption. The pressure formula is supplied in every pressure stage; do not infer that the density or average-speed formula is also supplied. Use a provided force in newtons, positive contact area, correct squared-area conversion and an explicitly limited average-pressure model. No real-world safety or route-feasibility certification follows. The source assessment context uses SI units and may require mathematical instruments. These lessons do not complete4.5 nearest-mm line drawing, formal shape/compass constructions or scale-drawing problems,5.2 transformations,4.8 bearing trigonometry,4.9/4.10 full mensuration or4.11 map/similarity work. No blanket formal-proof waiver is imported. Written practice is self-checked, not automatically marked; acknowledgements and attempts do not award marks or establish mastery. Specialist approval and formal assessment validation remain unestablished. Publisher navigation is separate evidence: literal F4.4D appears in Book2 Shape and Space6, map physical10/pages128–160, and Hub36 Bearings and Scale Drawings, co-tagged F4.5C/F4.11B; those co-tags confer no construction/map credit here. Literal F4.4G appears in Book1 Number5, map physical5/pages255–268, and Hub13 Compound Measures. A/B/C/E/F have no literal4.4 chapter or Hub tag in that map; do not invent one from nearby time or scale-drawing topics. Book1 public uncorrected-proof contents start Number5/Compound measures at256 and end its summary at269, conflicting with map255–268; preserve both references. Book2 chapter start128 and next start161 agree with its map range, but no explicit bearings contents heading locates every skill. Neither relevant chapter body is present in the public samples. Full final-book/Teaching Hub content and pagination alignment remain unverified; chapter links are not full-book or modular teaching credit. The current2026/2027 manual lists linear4MA1 F/H in November2026 and June2027; FR/HR are June2027 only, based on centre eligibility. Vietnam is on the regional-centre list; learner residence alone does not choose an option. The table points to page2 although the list is on physical/printed3. Modular4XMAF/4XMAH cash-ins and4WM units remain separate entries for international centres. This entry context does not create a2027 revision of the Issue2 specification.
Before you begin
- Identify an angle’s vertex and arms from its three-letter name.
- Recognise acute, right, obtuse, straight and reflex angle ranges.
- Subtract from 360° and round a decimal to the nearest whole number.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Where should the protractor’s centre be placed to measure ∠AOB?
What you will learn
- Align a protractor’s centre and baseline with the angle’s vertex and one ray.
- Read the zero scale that runs into the marked angle, including a tilted baseline.
- Distinguish approximate instrument readings from ideal references and identify a requested reflex arc.
Use the accurate labelled acute-angle diagram ∠AOB. The baseline ray OA points to the right and OB rises above it; the marked arc selects the small opening. Position a protractor, measure to the nearest degree, and explain the centre, baseline and scale you used. The rays are supplied without a numerical angle label; do the measurement before opening the reference.
Read, draw and calculate before comparing. Every requested part and explanation needs your own attempt. The teal protractor and orange rays show your actual placements, including wrong ones. Comparisons do not award marks or establish practical instrument competence.
Coordinates use the original worksheet grid. The entire drawing and your tools rotate together; clockwise bearings retain their direction. Case or orientation changes clear all responses, placements and references. Named given points can be placed exactly; other drawing clicks use the nearest half-unit grid point and never snap to a solution.
Given panel 1
The board retains the last submitted valid placement. Editing a draft invalidates its submission without moving the last drawing; submit again before comparison.
Place the centre and baseline accurately
Identify the angle’s vertex and the two rays that form its arms. Put the protractor’s centre exactly on the vertex, then align its baseline with one ray. Keep that alignment while reading the other arm. If a ray is too short to reach the scale, extend it along the same straight line; do not move the vertex or change its direction.
Work on a diagram explicitly supplied for measurement. A printed centimetre ruler needs physical calibration, but an angle can be measured on a uniformly enlarged or reduced diagram because its opening is unchanged. Unequal horizontal and vertical stretching changes that opening. A diagram labelled not to scale, or an exam diagram without permission to measure, is not a substitute for given angle facts.
Read from the correct zero
Many protractors print two number scales running in opposite directions. Find the zero at the baseline ray and follow the numbers that increase into the marked angle. Before choosing a reading, ask whether the opening is acute or obtuse: the wrong scale often gives the supplement, which should disagree with that visual check.
A tilted baseline works in exactly the same way. Rotate the protractor to align with the ray instead of reading from the page’s horizontal edge. Use the arc mark to decide which opening is requested. With a reflex angle, the marked opening is greater than 180°; a semicircular protractor can measure the smaller companion, which you then subtract from 360°.
Round a measurement, not an invented exact value
Read the scale and report the requested nearest whole degree with the ° symbol. For example, a reference model just above a whole-degree mark may round down, while one more than halfway to the next mark rounds up. Avoid claiming exactness from a broad line, a small print or a manually positioned tool; a measured result is an approximation.
The worked and practice figures have private ideal reference angles used after you have measured them. Those references help compare alignment and rounding, but are not numbers to copy before using the instrument. No universal automatic tolerance or specialist assessment of practical instrument skill is established here. Explain your placement and scale choice as well as writing a number.
Sources for this lesson
Pause and explain
Two rays have a smaller opening of 137°. The other arc marks a reflex opening. What is its companion?
Worked example
Use the accurate labelled acute-angle diagram ∠AOB. The baseline ray OA points to the right and OB rises above it; the marked arc selects the small opening. Position a protractor, measure to the nearest degree, and explain the centre, baseline and scale you used. The rays are supplied without a numerical angle label; do the measurement before opening the reference.
Show the worked solution
- Place the protractor centre on O and its baseline along the rightward ray OA. If necessary extend OB straight to the scale, without moving O.
- Use the scale whose zero lies on OA and whose values increase upwards into the marked small angle. The opening is acute, so a reading greater than 90° would signal the wrong scale.
- Read the crossing near 64°. The ideal reference opening is 64.4°, which rounds to 64° to the nearest degree; that reference is a check after measuring, not a substitute for the tool action.
- Report approximately 64° and describe the alignment. A physical reading may vary with drawing and placement, so use the reference to check those choices rather than claiming more precision.
Answer Reference nearest-degree measurement: 64°. Centre at O, baseline along OA, and the increasing scale from the right-hand zero.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Use the accurate obtuse ∠AOB diagram. OA is the leftward horizontal baseline ray and OB points to the upper right; the marked arc runs through the upper half-plane from OA to OB. Use a protractor to measure that opening to the nearest degree, and explain why the other scale’s reading is unsuitable. Do not use a numerical angle label as a shortcut.
Give me a hint
Start from the zero on the leftward baseline. Check that your chosen opening exceeds 90°.
Compare my reasoning
- Place the centre at O and align the baseline with the leftward ray OA. Keep the upper marked opening in view rather than the lower or reflex opening.
- Follow the protractor scale that starts at zero on OA and increases into the upper arc. The angle is obtuse, so the accepted reading must lie between 90° and 180°.
- The ideal reference opening is 126.6°, so the nearest-degree result is 127°. The opposite scale would give the acute companion near 53.4°, which is not the marked obtuse opening.
- Report about 127° and explain the centre, baseline and left-zero choice. Compare the reference only after your own instrument reading.
Reference measurement: 127° to the nearest degree. The other scale describes the acute supplement rather than the marked obtuse angle.
Look for these in your work
- Align the centre and the leftward baseline ray.
- Select the scale that begins at that ray’s zero and matches the obtuse arc.
- Record about 127° with a clear measurement explanation.
Measure the marked small ∠AOB on the fresh accurate diagram with a tilted baseline. Both rays point generally to the left, and the second lies below the baseline ray. Independently place and rotate the protractor, record a nearest-degree answer and describe one alignment check. The angle’s numerical reference is withheld until after the attempt.
Give me a hint
Rotate the tool to OA; the page’s horizontal edge has no role in defining this angle.
Compare my reasoning
- Locate O and align the protractor centre there. Rotate the baseline onto OA instead of leaving it horizontal on the page.
- Read the scale beginning at OA’s zero and running into the marked small arc. The opening is acute, so reject a large supplementary reading.
- The ideal reference opening is 39.3°. Rounding that comparison value to the nearest degree gives 39°; your task is to obtain a nearby instrument reading from the diagram first.
- State about 39° and describe how the centre remained at O while the baseline was aligned with the tilted ray. A different page orientation does not change the opening.
Reference nearest-degree measurement: 39°, using the tilted OA ray as the baseline.
Look for these in your work
- Perform the protractor placement independently on the tilted diagram.
- Choose the marked acute opening and the matching zero scale.
- Report about 39° and state a concrete centre or baseline check.
The accurate diagram shows the same two labelled rays OA and OB with two separately identified arcs: the smaller opening and the reflex opening. Measure and report both to the nearest degree. Explain how your protractor reading distinguishes the arcs, and why a reference value from the model should be checked after measurement rather than copied before it.
Give me a hint
The small and reflex openings make a full 360° turn. The reflex result must exceed 180°.
Compare my reasoning
- Place the centre at O, align with OA and measure the smaller marked opening. The ideal model gives 128.6°, so its nearest-degree reference is 129°.
- The reflex arc is the rest of the complete turn. For the ideal comparison, 360−128.6=231.4°, which rounds to 231°.
- A nearest-degree reading of 129° also gives the corresponding rounded companion 360−129=231°. State which value belongs to which arc and check that the reflex one exceeds 180°.
- Both answers are reported measurements. The reference model checks the diagram and rounding, while your centre, baseline and scale explanation shows the actual method.
Smaller opening: about 129°. Reflex opening: about 231°. Their unrounded ideal reference openings are 128.6° and 231.4°.
Look for these in your work
- Measure the requested smaller arc using the correct protractor alignment.
- Use a full turn to identify the distinct reflex companion.
- Label about 129° and about 231° without presenting a model value as prior practical measurement.
Common mistakes
- Placing the protractor centre away from the vertex or aligning the baseline to the page instead of the angle ray.
- Reading the scale that starts at the opposite zero, so an acute angle is mistaken for its obtuse supplement.
- Ignoring a reflex arc, claiming an exact measurement, or measuring a not-to-scale diagram without permission.
What can you explain now?
A marked angle is obtuse, but a student reads 59° from one protractor scale. The other scale reads 121°. What should be checked?
Compare with the explanation
Check the centre and baseline, then use the scale starting at the aligned ray’s zero; the obtuse reading is about 121°.
The two scales can show supplementary values, 59°+121°=180°. The requested obtuse opening must exceed 90°, so 59° is inconsistent with that arc if placement is correct.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain the three placement choices—vertex, baseline and zero scale—and one acute/obtuse check. Then explain how to obtain a reflex opening from a measured smaller companion.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.