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Session 7: Unit Conversion I

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Session 7

Unit Conversion I

Your Caliper Has a Switch

Inches on one side, millimeters on the other.

Real hardware doesn't always come in the unit you're thinking in.

Why This Matters

Ordering the wrong size fastener. Misreading a spec sheet. Real consequences — not an abstract math worksheet.

Why This Matters

Every conversion in this course uses real shop specs, not km-to-miles style problems.

The Conversion Factor

A fraction that equals 1 — like 25.4 mm / 1 in.

Multiplying by it changes the units, not the actual size.

Setting It Up

Orient the fraction so the unit you don't want cancels out, leaving the unit you do want.

Worked Example

Let's put a number on Session 1's ramp: say it used 3/8 in plywood. What's that in millimeters?

Worked Example

0.375 in × (25.4 mm / 1 in)

Worked Example

0.375 in × (25.4 mm / 1 in) = 9.525 mm

The "in" units cancel. Only "mm" is left.

It's Not Just the Number

Show your conversion factor and your units at every step.

A correct final answer with no shown work doesn't count as done correctly — setup matters as much as the number.

Two Things to Remember

Units cancel like fractions.

If you can't visually cross out the unit you started with, your setup isn't finished yet.

Two Things to Remember

Wrong units left over means the factor is upside down.

Flip the fraction and try again — don't just force the division.

Next Time

Session 8: Unit Conversion II

Chaining multiple conversions together in one problem.

'F' → Fullscreen

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Build

Worked Example, Full Setup

3/8 in plywood, converted to millimeters:

StepWork
Start0.375 in
Conversion factor× (25.4 mm / 1 in)
Units cancelin cancels, mm remains
Answer9.525 mm

Your Turn: Real Shop Conversions

For each problem, show your conversion factor, show your units canceling, and state your final answer with units.

  1. A bolt spec calls for a 1/2 in diameter. What's that in millimeters?
  2. A hex key is labeled 10 mm. What's that in inches (decimal)?
  3. A different sheet of plywood is 3/4 in thick — twice the thickness of the ramp's. What's that in millimeters?
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Checkpoint

Before you submit, check each problem for all three:

  • Your conversion factor is written as a fraction, with units
  • The unit you started with is visibly canceled, not just dropped
  • Your final answer includes the correct remaining unit

A right number with no shown setup, or a setup with the units canceling backward, isn't complete — even if the final number happens to look reasonable.

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Reflection

Answer the following questions before submitting your work.

  1. Which of today's problems felt most like something that could actually happen in a real shop? Why?
  2. Can you get lucky and land on the right final number with a wrong setup? What would that look like?
  3. Session 8 chains multiple conversions together in one problem. Can you think of a shop situation where you'd need to convert through two different units to get your answer, not just one?
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Submit

Submit your conversion problem set and your reflection.

Activity Complete