Grave accent

Did you notice how the accent changed on ἐγώ in the phrase ἐγὼ εἰμί? Instead of going up the accent goes down.

The accent that goes up (ἐγώ) is called an acute accent.
The accent that goes down (ἐγὼ) is called a grave accent.

This change doesn't effect how you say the word; you still place stress on the accented syllable. and it has no effect on the meaning of the word.

Here is the rule: if the final syllable of a word is accented with an acute, and if the word is not followed by punctuation, then the acute is changed to a grave. So if ἐγώ were the final word in a sentence, the acute accent would remain.

Interesting: the reason for this is because the accents used to indicate musical pitch. An acute meant the voice went up in pitch, and the grave indicated that the pitch went down. (This is why their shapes go up and down.) The Greek speaking pattern was that the voice would tend to drop in pitch after each word as they were speaking, until they came to the end of sentence at which time the pitch went up. In English, we raise the pitch of our voice at the end of a question. Greek was the opposite.