Morten St George Theory

[Morten St. George]

The plus sign existed in the 15th century in the senses of "positive quantity", "and", and "add":

• Here is an example from a printed book from the 1480s showing surfeits and deficits from Widmann's Mercantile Arithmetic. The minus sign is longer than the modern version, but the plus sign is the same as the one we use today:



Widmann apparently also taught these symbols to his students (they've been found in one of his students' notebooks).

• The plus sign in the sense of "and" (rather than the traditional ampersand) existed in the 14th century in one of the copies of  Oresme's mathematical treatise, Algorismus proportionum, 1360.

• The plus sign in the sense of "add" or "add here" was used in the 15th century to mark sections where the rubricator was supposed to add an embellished initial.

I figured you would find something. You usually do. I think you should write to Google and inform them that they are providing an incorrect response to the question When was the plus sign invented?

Still, 1489 is not 1404-1438 and there appears to be little evidence that the plus sign was widely used (or even known at that time) anywhere outside of a single place in Germany which, by the way, is not Italy.

Are you now willing to concede that the marginalia was likely written after completion of the VMS?