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Opens on Chapter 8’s example: Millbrook’s coffee shops (12 to 18) and bike commuters (3,100 to 3,600) over eight years.
The dual-axis trick
Enter your numbers, then press Calculate.
How it works
Divide every value by the series’ first value and multiply by 100: both lines start at 100, and a line at 150 has grown 50%. Any right-axis range can make two lines meet, cross or run together, which is why the crossing point on a dual-axis chart means nothing.
From the book, Chapter 8. Indexed to 100, the coffee shops end at 150 (50% more) and the commuters at 116.1 (16.1%). Commuters per shop fell from 258 to 200. A right axis from 2,933 to 3,767 would lay the two raw lines on top of each other. Every chapter and its calculator →
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