What counts as a full rep pull-up?
Some will say chin over the bar, others will argue chest over the bar.
However these are just, arbtirary answers that are just based on convenience of measurement.
The full range of motion of the pull-up, should be the full range that is anatomically capable.
That include complete depression and retraction of the scapula and your elbows as far back as possible.
That was what Vince Gironda thought, after seeing plenty of sloppy half ref pull-ups at his own gym back in the 70s
“The biggest mistake I have observed in lat work is not completing the movement or full contraction. This habit produces a flat back with no trapezius development or thickness." - Vince Gironda
What are sternum pullups?
Sternum pullups are a variation of pullup that work the entire range of movement of the pullup.
You start from a dead hang and end at a full retract and depression of your scapula and arms pulled back as far as possible until your sternum touches the bar.