"...when the less of the numbers AB and CD being continually subtracted from the greater, some number is left which measures the one before it."
2,400 years and translation first to words and then to another language are, admittedly, not kind to an algorithm taken out of context. So, let's look at an example.
If AB is 345, for instance, and CD 943, we'll start by subtracting 345 (the lesser number) from 943 to get 598 for a new pair of 345 and 598; subtracting, now, 345 from 598 gets us 253 and the pair 345 and 253; onward similarly: 345-253=92; 253-92=161; 161-92=69; 92-69=23; 69-23=46;46-23=23.
The final pair is 23 and 23. In easy and elegant a fashion, Euclid's algorithm, possibly the oldest still in use today, has offered us the "measure" or (greatest common) divisor of 345 and 943: 23.
For the greatest common Mac OS X Mail add-on, let's try a different algorithm: adding up the most popular tools and plug-ins.
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