Today I learned that the size and shape of a punch card
was chosen to be the same as US paper money at the time.
At the time a US bank note had dimensions 3.25″ by 7.375″. This was sometime prior to 1929 [1] when the size of a bank note changed to 2.61″ by 6.14″. Here’s a current US dollar to scale.
Thinking about how US bank notes shrank in size made me think about how they shrank in purchasing power as measured by the Consumer Price Index. I chose 1861 as my baseline because that’s when the US chose the bank note dimensions above.
Here’s a plot.
Curiously, the ratio of purchasing power to area in 1940 almost returned to what it had been in the 1800s.
In 2025, $1 has about 3% of the purchasing power of $1 in 1861. To maintain the same purchasing power per square inch, a $1 note in 2025 should have an area of 0.72 square inches. To maintain the current aspect ratio, this would be 0.55″ by 1.3″.
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[1] Punch cards have been around longer than electronic computers. Their first large-scale application was tabulating the 1890 US census.
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