A MIDI note number of 60 is "Middle C" on a piano. So, a MIDI note number of 69 is used for A440 tuning.

Allowable values for MIDI note numbers are 0 to 127 (ie, there are a maximum of 128 different notes that a MIDI instrument can possibly play).

Most software doesn't use MIDI note numbers to identify notes to a musician (even though that's what the MIDI gear expects, and what the software sends to it). MIDI note numbers don't mean much to a musician. Instead, the software identifies a note in "musical terminology" such as saying that the note is the F# in the third octave (of a piano keyboard). So, that note is F#3. If your MIDI unit (or software) considers octave 0 as being the lowest octave of the MIDI note range, then middle C is C5. The lowest note is then C0 (note number 0), and the highest possible note is G10 (note number 127). Some units consider the 3rd octave of the MIDI note range (ie, 2 octaves below middle C) as octave 0, and therefore, the first 2 octaves are referred to as -2 and -1. In this case, middle C is identified as C3, the lowest note is C-2, and the highest note is G8.