Six Ciphers, One Word
Type a name into the calculator and it returns six different numbers. Which one gets quoted is a choice made after the numbers are known, and that is the whole mechanism behind reading meaning out of letters.
What you are looking at
The calculator above computes a word's value under six schemes at once. The traditional Hebrew reckoning, Greek isopsephy, and the four English ciphers the modern practice uses.
English has no inherited numbering of its letters, which is why there are several English ciphers rather than one. That isn't a flaw in somebody's method. It is the method.
Try it with a name
Type any phrase and watch the column of totals. A single English phrase doesn't have a value. It has four, and they're rarely close together. Add the choice of which spelling to use, full name or surname or nickname, with or without a title, and one subject offers dozens of numbers before anybody has decided what counts as significant.
Under those conditions a match isn't surprising. It's what the arithmetic predicts.
The part that isn't arbitrary
The Hebrew examples are different and worth pressing the buttons for. The 318 armed men of Genesis 14:14 really is the value of the name Eliezer. Neron Kesar in Hebrew letters really does total 666, and the shorter Latin spelling really does total 616, which is what some of the earliest surviving manuscripts of Revelation read instead.
That last pair is the one case here where the number moves when the spelling moves, and moves exactly where the spelling predicts. Nobody had to pick a cipher to make it work.
The full account is in the archive: Gematria and the Hidden Meaning of Numbers.