Hi guys this is my first post so forgive me if it's been posted before or it's in the wrong place. Basically I am trying to tune my guitar a half step down. I have a chromatic tuner, a Boss TU-80 and i'm pretty confused as to how it works. When i set it to the chromatic setting and hit the strings they come up with a number i.e. e3 what do these numbers represent and how do i tune it a half step down. I know E will go to e flat etc but what numbers should i be looking for?

I hope this makes sense