MIDI : Pitch Bend

[Muxlow]

Let's say that I want to bend a MIDI note up one half step. I don't have a MIDI input device with a wheel to dial it in in real time, so I'm using the pencil and editing the track's Pitch Bend. This is where I get lost...

How exactly is that line measured? An unbent note's Pitch Bend line sits as zero, and when I use the pencil to 'bend' the line up, it jumps in seemingly random increments that move very quickly (it'll jump hundreds with the tiny bump of the mouse). So how many of these 'points' make up a semi-tone?

Oh, and don't say "use your ears". I need precision and want to understand how this works.

Thank!