What a misplaced decimal point costs

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What the video covers, what to say before it, where a class usually goes wrong, and what to set afterwards. An account is free, and it opens every chapter of every book.

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What to assume they know

Extending Indian place value to the right of the point — the point as the marker of where the units place ends (Part I, §3.4)
Why measurement units are built in tens — the metric and money relations, and converting between units (Part I, §3.5)
Adding and subtracting decimals by aligning place value — estimating a sum before computing it (Part I, §3.7)
Multiplying and dividing a decimal number by 10, 100 or 1000, informally
Reading a quantity aloud with its unit attached

What they should be able to do

State the two things a digit string needs before it names a quantity
Describe each of the three incidents the chapter reports, and identify in each one which anchor was lost
Work out the factor by which an answer is wrong when a digit is read one place out
Distinguish an error of place from an error of unit, and say why the chapter files them together
Explain why an error of this kind is disproportionate to how small it looks on the page
Name two checks that catch such an error before it is acted on

Where it usually goes wrong

"A decimal point error is a small error." It is a multiplication, not a nudge. The dose is out by exactly ten and the Amsterdam payment by around a hundred; even the fuel case, the mildest of the three, is out by a factor near two and still nearly cost an aircraft. The section exists to make that unforgettable.
"These are computer failures, not arithmetic ones." In each case a machine or a person handled the digits correctly. What went missing was the meaning attached to them.
"All three are point errors." Only the dose is. The Amsterdam case is a unit confusion between euros and cents, and the fuel case is a unit confusion between pounds and kilograms with no point involved at all. The chapter groups them under a heading that names decimals and measurement together, and reports the fuel case as a decimal error; say what the printed page says, and then draw the distinction, rather than pretending the three are the same shape.
"Getting the unit wrong is always a factor of ten." The fuel case is not: pounds against kilograms is a factor near two. It is still an anchor failure, and it still nearly destroyed an aircraft.
"Someone would notice a number that wrong." In two of the three cases nobody did until the consequence arrived. That is the argument for checking before acting, not after.
"Rounding causes this." Rounding shortens a number by a little. These errors relocate it. Keep the two apart, especially since Part I, Chapter 1 spent a section on honest approximation.

Questions to check understanding

Given a quantity and a stated unit error, work out the factor by which the answer is wrong
Convert a quantity between two units and check the answer against a rough estimate
Given a computed answer that is out by a power of ten, find the place slip that produced it
Explain why a number written without its unit cannot be checked
Rewrite a quantity in a smaller unit and say how the digits move
Describe one of the chapter's incidents and identify what was lost

Examples worth working on the board

Amsterdam, 2013 (Part I, §3.8, p.77). The city council's finance office sent out housing benefits of €188 million where €1.8 million was intended, because the payment run was processed in euro cents rather than in euros. The chapter supplies the relation as one euro-cent being a hundredth of a euro. Take both money figures as printed inputs and do not derive one from the other — see Notes.
Air Canada, 1983 (Part I, §3.8, p.77). A Boeing 767 was loaded with 22,300 pounds of fuel where the figure was meant to be in kilograms. The chapter gives the conversion as one pound being about 0.453 kg and describes the result as roughly half of what was required. The aircraft ran out of fuel in flight and landed at a disused airfield; nobody was hurt.
A dose read one place out (Part I, §3.8, p.77). 0.05 mg read as 0.5 mg. The chapter states plainly that this is ten times the prescribed amount, and notes that incidents of this kind have happened more than once in medicine.
The chapter's closing instruction (Part I, §3.8, p.77). Attention is owed to the units and to where the point sits.
The reading convention that helps (Part I, §3.4, p.63). A decimal number is said one digit at a time after the point, so 0.05 and 0.5 sound nothing alike when spoken correctly. This link is added here to make; the chapter does not join the two passages.

Figures to have open

Two bars for the intended and the actual payment. Standard schematic. Draw them honestly, at whatever ratio the two printed figures actually stand in.
A place value strip with one digit that can be dragged one column left or right, and the value read off underneath. Standard schematic; it is the single reusable graphic of this topic and serves sections 3, 6 and 8.
A fuel gauge or a tank filled to two different levels, one for the figure loaded and one for the figure required. Standard schematic.
A vertical ladder of powers of ten. Standard schematic.
No photograph is required, and nothing on p.76 needs redrawing — that page is text and question prompts only, checked against the printed page. But p.77 does carry artwork: an unnumbered three-panel cartoon under "Deceptive Decimal Notation", in which a mis-stated door width produces a door that will not close. It is not a diagram in the mathematical sense and nothing is measured off it, so an explanation may retell the incident in its own artwork rather than reproduce the panels — but it must not be described as a page without a figure.

Where this sits in the book

NCERT Ganita Prakash, Class 7, Part I, printed Chapter 3 "A Peek Beyond the Point", §3.8 More on the Decimal System, opening on p.76, and its first unnumbered subheading Decimal and Measurement Disasters, whose two bulleted incidents and closing paragraph run from p.76 onto p.77.
Backward pointers: Part I, §3.5, pp.64–69, for every unit relation used here; Part I, §3.4, p.63, for reading a decimal number aloud; Part I, §3.7, p.76, for the note that estimating first can expose a wrong answer.
Forward pointer inside the same section: Part I, §3.8, pp.77–78, on notation that looks decimal and is not.