How to speed up writing before the computer age. This suggestion of writing with 2 quills came from a schoolmaster and was formulated in 1692 Nuremberg, Germany. #skystorians
You may find this image, and the explanation how to write 2 letters at once, in here: digital.slub-dresden.de/werkansicht/...

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“Write twice as fast as the next door writer! Win the race of speed with our double-headed quill”
The later copy and fax machines ruined it all for this invention!
Why not buy 2 and write with both hands? You'll have 4 identical letters in no time!
A trained hand of a multitasking hero might have written 2 different letters at the same time.