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A digital micrometer gives you a number. But is that number the object's

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true width? Let's find out by measuring, checking the scales, and correcting zero

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error.

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Start in Explore. You can see the digital display and use guided hints.

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Practice hides the display until you answer correctly. Challenge gives you a new

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measurement and a random zero error.

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The green rectangle is your object. To increase its width, drag the small

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square at its bottom right to the right. Watch the object grow while

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the spindle stays still.

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Now pull the thimble to the left. This moves the spindle towards the

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object. Stop at contact. The fixed anvil and moving spindle must touch opposite

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sides of the object before you read its width.

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Our object measures seven point six six millimetres. Let's check the scales. Read

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the last visible sleeve mark before the thimble edge. Include the half millimetre

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mark: the sleeve contributes seven point five zero millimetres.

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Next, find the thimble division that lines up with the sleeve reference line.

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Sixteen divisions at zero point zero one millimetres each give zero point one

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six millimetres. Add the two readings: seven point six six millimetres.

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Choose Practice from the mode menu. The digital answer disappears, so you do

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the thinking. The object and scale reading stay the same. Try reading them

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yourself before asking for help.

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Need a nudge? Open the same menu and choose Hint, next step. The

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hints guide you through the reference line, sleeve, thimble, and zero error. Ask

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for one step, then do that step yourself.

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For desktop use, choose text input. Enter seven point six six, and press

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Check. Use millimetres and two decimal places. A correct answer reveals the display

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and the worked calculation, so you can check your method.

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On a phone or tablet, landscape gives the instrument more room. Tap Input,

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text to switch to the answer list. Select your reading, then press Check.

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This avoids typing with a small on-screen keyboard.

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Tap the input control again to return to text entry. The choice is

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yours on either device. It is a manual toggle, so a desktop can

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use the list and a mobile device can use text.

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Before trusting a measurement, check zero error. With no object between the faces,

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a correctly zeroed micrometer reads zero when closed. Choose an offset with the

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zero error menu. Read the sleeve and thimble scales for the observed reading.

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Then subtract the signed zero error to find the corrected width.

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Choose a positive zero error of zero point one zero millimetres. Our object

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has not changed, but the observed reading rises to seven point seven six.

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The instrument is reading too high.

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Corrected reading equals observed reading minus zero error. Seven point seven six minus

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positive zero point one zero gives seven point six six millimetres. Enter the

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corrected reading, not the uncorrected number on the scale.

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Now choose negative zero point one zero millimetres. The observed reading drops to

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seven point five six, even though the object is still the same width.

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Pause here. Should the correction make this reading larger or smaller?

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It must become larger. Subtracting a negative means adding. Seven point five six

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minus negative zero point one zero gives seven point six six millimetres. Keep

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the sign inside brackets, and the same rule works for both errors.

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Ready to test yourself? Choose Challenge. It creates a new object width and

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random zero error. The zero error selector is locked, and hints stay locked

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until you make one attempt. Read the scales and account for the displayed

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zero error.

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An incorrect attempt is useful evidence. Here, we deliberately enter zero to see

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the feedback. Now a hint is available. Work through the reading and correction,

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then submit your revised answer.

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Press New challenge for another measurement. Don't reuse the old answer. Check the

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new sleeve reading, thimble division, and zero error every time.

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Teachers, model one example in Explore, let pairs explain their steps in Practice,

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then use Challenge for an independent check. Students, try the same object with

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positive and negative zero error. Can you prove that its corrected width stays

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the same? Open the simulation linked below and give it a go.