[
  {
    "chapter": "Can you trust the display?",
    "title": "Can you trust this reading?",
    "card": "A number on a screen is only the start.",
    "text": "A digital micrometer gives you a number. But is that number the object's true width? Let's find out by measuring, checking the scales, and correcting zero error.",
    "action": "intro",
    "duration": 11.798666666666668
  },
  {
    "chapter": "Explore: resize and measure",
    "title": "01 / EXPLORE",
    "card": "Explore  >  Practice  >  Challenge",
    "text": "Start in Explore. You can see the digital display and use guided hints. Practice hides the display until you answer correctly. Challenge gives you a new measurement and a random zero error.",
    "action": "orient",
    "duration": 13.868
  },
  {
    "title": "Make the object wider",
    "card": "Drag the small square at the bottom-right corner.",
    "text": "The green rectangle is your object. To increase its width, drag the small square at its bottom right to the right. Watch the object grow while the spindle stays still.",
    "action": "resize",
    "duration": 12.417333333333334
  },
  {
    "title": "Bring the spindle into contact",
    "card": "A gap means you are not measuring the object yet.",
    "text": "Now pull the thimble to the left. This moves the spindle towards the object. Stop at contact. The fixed anvil and moving spindle must touch opposite sides of the object before you read its width.",
    "action": "close",
    "duration": 14.273333333333333
  },
  {
    "title": "Read the sleeve first",
    "card": "Sleeve: 7.50 mm",
    "text": "Our object measures seven point six six millimetres. Let's check the scales. Read the last visible sleeve mark before the thimble edge. Include the half millimetre mark: the sleeve contributes seven point five zero millimetres.",
    "action": "sleeve",
    "duration": 16.662666666666667
  },
  {
    "title": "Then read the thimble",
    "card": "7.50 mm + 0.16 mm = 7.66 mm",
    "text": "Next, find the thimble division that lines up with the sleeve reference line. Sixteen divisions at zero point zero one millimetres each give zero point one six millimetres. Add the two readings: seven point six six millimetres.",
    "action": "thimble",
    "duration": 17.046666666666667
  },
  {
    "chapter": "Practice: hints and answers",
    "title": "02 / PRACTICE",
    "card": "Read first. Commit to an answer. Then check.",
    "text": "Choose Practice from the mode menu. The digital answer disappears, so you do the thinking. The object and scale reading stay the same. Try reading them yourself before asking for help.",
    "action": "practice",
    "duration": 13.441333333333333
  },
  {
    "title": "A hint, one step at a time",
    "card": "Mode menu  >  Hint: next step",
    "text": "Need a nudge? Open the same menu and choose Hint, next step. The hints guide you through the reference line, sleeve, thimble, and zero error. Ask for one step, then do that step yourself.",
    "action": "hint",
    "duration": 13.718666666666667
  },
  {
    "title": "Desktop: type your answer",
    "card": "Type 7.66  >  Check",
    "text": "For desktop use, choose text input. Enter seven point six six, and press Check. Use millimetres and two decimal places. A correct answer reveals the display and the worked calculation, so you can check your method.",
    "action": "answer",
    "duration": 16.236
  },
  {
    "chapter": "Mobile list and desktop text",
    "title": "Your device. Your choice.",
    "card": "Tap Input: text to switch to Input: list.",
    "text": "On a phone or tablet, landscape gives the instrument more room. Tap Input, text to switch to the answer list. Select your reading, then press Check. This avoids typing with a small on-screen keyboard.",
    "action": "mobile",
    "duration": 15.148
  },
  {
    "title": "Switch back whenever you like",
    "card": "The switch is manual: both options remain available.",
    "text": "Tap the input control again to return to text entry. The choice is yours on either device. It is a manual toggle, so a desktop can use the list and a mobile device can use text.",
    "action": "desktop",
    "duration": 13.910666666666666
  },
  {
    "chapter": "Positive zero error",
    "title": "Zero error: first check the zero",
    "card": "Corrected reading = observed reading - zero error",
    "text": "Before trusting a measurement, check zero error. With no object between the faces, a correctly zeroed micrometer reads zero when closed. Choose an offset with the zero error menu. Read the sleeve and thimble scales for the observed reading. Then subtract the signed zero error to find the corrected width.",
    "action": "zeroIntro",
    "duration": 21.654666666666667
  },
  {
    "title": "Positive error: reading too high",
    "card": "Positive zero error: +0.10 mm",
    "text": "Choose a positive zero error of zero point one zero millimetres. Our object has not changed, but the observed reading rises to seven point seven six. The instrument is reading too high.",
    "action": "positive",
    "duration": 15.105333333333334
  },
  {
    "title": "Subtract the positive error",
    "card": "7.76 - (+0.10) = 7.66 mm",
    "text": "Corrected reading equals observed reading minus zero error. Seven point seven six minus positive zero point one zero gives seven point six six millimetres. Enter the corrected reading, not the uncorrected number on the scale.",
    "action": "positiveAnswer",
    "duration": 17.58
  },
  {
    "chapter": "Negative zero error",
    "title": "Negative error: reading too low",
    "card": "Negative zero error: -0.10 mm",
    "text": "Now choose negative zero point one zero millimetres. The observed reading drops to seven point five six, even though the object is still the same width. Pause here. Should the correction make this reading larger or smaller?",
    "action": "negative",
    "hold": 3,
    "duration": 19.833333333333332
  },
  {
    "title": "Subtracting a negative means adding",
    "card": "7.56 - (-0.10) = 7.66 mm",
    "text": "It must become larger. Subtracting a negative means adding. Seven point five six minus negative zero point one zero gives seven point six six millimetres. Keep the sign inside brackets, and the same rule works for both errors.",
    "action": "negativeAnswer",
    "duration": 17.9
  },
  {
    "chapter": "Challenge: attempt, reflect, repeat",
    "title": "03 / CHALLENGE",
    "card": "Random width. Random zero error. Your first attempt.",
    "text": "Ready to test yourself? Choose Challenge. It creates a new object width and random zero error. The zero error selector is locked, and hints stay locked until you make one attempt. Read the scales and account for the displayed zero error.",
    "action": "challenge",
    "duration": 17.516
  },
  {
    "title": "Use feedback to improve",
    "card": "Attempt  >  feedback  >  hint  >  corrected answer",
    "text": "An incorrect attempt is useful evidence. Here, we deliberately enter zero to see the feedback. Now a hint is available. Work through the reading and correction, then submit your revised answer.",
    "action": "challengeAnswer",
    "hold": 4,
    "duration": 18.273333333333333
  },
  {
    "title": "One more, independently",
    "card": "New challenge  >  a fresh measurement",
    "text": "Press New challenge for another measurement. Don't reuse the old answer. Check the new sleeve reading, thimble division, and zero error every time.",
    "action": "newChallenge",
    "duration": 11.201333333333332
  },
  {
    "chapter": "Your classroom challenge",
    "title": "Measure. Explain. Prove it.",
    "card": "Same object. Different zero errors. Same corrected width.",
    "text": "Teachers, model one example in Explore, let pairs explain their steps in Practice, then use Challenge for an independent check. Students, try the same object with positive and negative zero error. Can you prove that its corrected width stays the same? Open the simulation linked below and give it a go.",
    "action": "outro",
    "duration": 21.142666666666667
  }
]