Decidial British currency converter - photo

[Altair]

Decidial British currency converter from the early 1970s. Used for converting pre-decimal pounds, shillings, and pence to decimal currency.

Fullsize image: https://s3-us-west-1.amazonaws.com/h...l_fullsize.jpg



More:

https://en.wikipedia.org/wiki/Decimal_Day


Previously:

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English/metric measurement error in the Mars Climate Orbiter
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Polishing a tarnished coin - GIF
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[mklotz]

The required equation is...

N = 100*(S/20 + D/240)

where:

N = new pence
S = shillings
D = old pence

The equation reduces to...

N = 5*S + D/2.4

Plugging the 4/11 from the photo into this yields:

N = 5*4 + 11/2.4 = 20 + 4.583333... = 24.583333...