Jastrow derives gematria from grammateia, meaning figures in financial records, or numbers written as symbols rather than by their names. The usage in Greek fits well. You are still right in away. If one column of amounts has 3 + 4 + 5 and another has 1 + 2 + 9, the totals will be the same. Your dour informant is half right. Saying the two words have the same value is the usual way of putting it; but it is part of the gematria technique to find two words of equal value, such as snake and Messiah.
I forgot to mention before that in Jastrow’s entry for gematria you will find an attestation of an inscription in Atbash code.
The Mystery I've Solved
50 cm Seat /147 cm Tall Throne
Ancient Witness to the Size of the Throne
The Relative Size of the Alexandrian Throne of St Mark
Ancient Confirmation of Mark's "Smallness"
Marcion and the Episcopal Throne
Where was Marcion's Throne?
Burning of Arian Books After Nicaea
Drawing on vellum. From MS CLXV, Biblioteca Capitolare, Vercelli, a compendium of canon law produced in Northern Italy ca. 825
A Fourth Century CE Marcionite Synagogue in Syria
Adversus Marcionem 1.19 and Antoninus Pius's Alexandrian "Zodiac Coins" of 144/145 CE
First Argument for the Alexandrian Origins of Marcion
Second Argument for the Alexandrian Origins of Marcion
Third Argument for the Alexandrian Origins of Marcion
Fourth Argument for the Alexandrian Origins of Marcion
Fifth Argument for the Alexandrian Origins of Marcion
Conclusion
Bonus
First Piece of Evidence
Second Piece of Evidence
Third Piece of Evidence
Preliminary Conclusion
Overriding Point
Bottom Line
In Summa:
Last Word
