"How many double visits did you do this month?"
I used to open my coaching reviews with that question. It measures the manager's diary, not the rep's progress.
A well-known model for evaluating training separates what people learned from what they actually do afterwards. I apply the same idea to coaching.
Four things I look at for each rep:
Sessions held. Double visits and debriefs. This is my effort, not their change.
Skill agreed. One named skill, in the rep's own words.
Skill seen on calls. On my later visits, did I see it used without a prompt?
Doctor response. Did the call change? A real question from the doctor, a trial, a next appointment.
The third one is the one that matters. If the skill never shows up on a call, the coaching did not work, however many sessions I held.
Two cautions.
Sales follow later and have many causes. I do not judge a skill on one month's number.
And the rep sees these too. It is their progress, not a report about them.
“Count the behaviour you saw, not the sessions you held.”

Lesson 20 of 23 in Step 4: Coaching, with the full guide and a checklist for this week.